RELATING CONSUMER EVALUATION OF APPLE FRESHNESS TO … · RELATING CONSUMER EVALUATION OF APPLE FRESHNESS TO SENSORY AND PHYSICO-CHEMICAL MEASUREMENTS S. PÉNEAU 1, P.B. BROCKHOFF2,

RELATING CONSUMER EVALUATION OF APPLE FRESHNESSTO SENSORY AND PHYSICO-CHEMICAL MEASUREMENTS

S. PÉNEAU1, P.B. BROCKHOFF2, E. HOEHN3, F. ESCHER1 and J. NUESSLI1,4

1Institute of Food Science and NutritionETH Zurich

Schmelzbergstr. 9, 8092 Zurich, Switzerland

2Informatics and Mathematical ModellingTechnical University of Denmark (DTU)

Richard Petersens PladsKongens Lyngby, Denmark

3Agroscope, FAW WädenswilSwiss Federal Research Station for Horticulture

Wädenswil, Switzerland

Accepted for Publication September 15, 2006

ABSTRACT

The objective of the present investigation was to elucidate sensoryattributes that influence consumer perception of apple freshness. A total of4,758 consumers rated the freshness of six apple cultivars stored at differentconditions. The apples were further characterized by consumer and panelsensory analyses as well as by physico-chemical analyses. The contributionof these characteristics to freshness was tested with principal componentregression. Texture properties were shown to be of main importance forfreshness, and flavor attributes of less importance. It is hypothesized that theevaluation of freshness might be a measurement of apple aging through theevaluation of its texture. Consumers of different age and levels of appleconsumption did not vary in their perception of freshness. However, differ-ences by gender were observed. Attributes shown to influence freshness werein agreement when measured by consumer, panel and physico-chemicalanalyses.

4 Corresponding author. TEL: +41-44-632-66-34; FAX: +41-44-632-11-23. EMAIL:[email protected]

Journal of Sensory Studies 22 (2007) 313–335. All Rights Reserved.© 2007, The Author(s)Journal compilation © 2007, Blackwell Publishing

313

mailto:[email protected]

PRACTICAL APPLICATIONS

Freshness is an important characteristic of fruits and vegetables. A betterunderstanding of what freshness means to consumers helps in the provision ofhigh-quality products perceived as fresh. A key finding of this study, whichconcentrates basically on the sensory aspects of freshness, is that freshness incase of apples is mainly related to high textural quality. Providing consumerswith apples that meet their expectations of a fresh product might increaseconsumption.

INTRODUCTION

Freshness is a decisive attribute for consumer choice of fruits and veg-etables (AgV 1981; Zind 1989, cited in Shewfelt 1990; Wandel and Bugge1997; Babicz-Zielinska and Zagorska 1998; Ragaert et al. 2004). However,although this attribute is clearly of importance to consumers, knowledge onhow consumers perceive freshness of fruits and vegetables and how theyunderstand this term is still limited. For this reason, the importance as well asthe perception of freshness of apples was investigated within the framework ofan exhibition on food during which 4,758 visitors completed a questionnaire(Péneau et al. 2006). The corresponding result showed that freshness, togetherwith taste and aroma, was a decisive attribute for selecting apples. When thesame consumers were asked to rate the importance of different attributes forthe evaluation of freshness, consumer perception of freshness was bestdescribed by taste, crispness and juiciness. Other aspects, including appear-ance, storage time, nutritional value and organic production, were of lessimportance. When, again, the same consumers had to rate the freshness, likingand sensory characteristics of an apple presented to them, freshness was shownto be related to crispness, juiciness, aroma and liking, in that order of impor-tance. We concluded that sensory quality and in particular textural character-istics contribute essentially to the perception of the freshness of apples.

Repeated attempts have been made to find indicators for freshness offruits and vegetables. Schwerdtfeger (1979) discussed the potential of markersas indicators of freshness and stated that such substances have to be involvedin catabolic processes that start soon after harvest. He concluded that apartfrom visual inspection of turgescence and plant color, no objective methodexisted for the evaluation of plant freshness at that time. On the other hand,Mermelstein (2001) stated that many constituents could be measured withquantitative instrumental or sensory tests to assess the “technically definedfreshness” of a food product. Different constituents have been proposed asindicator substances, such as measurements of propanethial S-oxide formation

314 S. PÉNEAU ET AL.

in scallions (Yamane et al. 1994), of asparagine concentration in the tip ofasparagus (Hurst et al. 1998), of chlorophyll fluorescence in broccoli(Toivonen 1992) as well as the evaluation of shear stress of guavas (Mandhyan1999). Shrivelling, pitting and decay of tomatillos (Cantwell et al. 1992),turgidity and green color of strawberry calyx (Saks et al. 1996) and, finally,measurement of overall appearance, hypocotyl color and texture and cotyledoncolor of bean sprouts (DeEll et al. 2000) were used to measure freshness witha sensory approach. These authors have selected attributes that, in theiropinion, were best associated with freshness or loss of freshness of a product.However, in all cases the term fresh was not based on consumer evaluation.

A first approach to improving understanding of the sensory factors thatinfluence the perception of freshness was to link freshness ratings with con-sumer sensory profiles of the same apple samples (Péneau et al. 2006). Col-lecting sensory profiles from consumers is accepted and frequently practiced(Elmore et al. 1999). However, if practiced, it assumes that all attributesselected are relevant to each consumer, that no other attributes are relevant tocertain groups of consumers and that consumers attach the same meaning to anattribute (Steenkamp et al. 1994). As these conditions could not be guaranteedin this experiment, it was considered important to test this perception withmore objective methods.

In the present experiment, apples that were rated for freshness by con-sumers, as described by Péneau et al. (2006), were also characterized by adescriptive sensory panel and by physico-chemical analyses. The main objec-tive of this investigation was to assess product characteristics that influenceconsumer perception of freshness in apples. As consumers of different age,gender and apple consumption were shown to have different perceptions offreshness (Péneau et al. 2006), the influence of these factors on sensoryattributes influencing freshness were also investigated. Finally, the character-istics revealed to be important for freshness when evaluated by consumers,a panel and by physico-chemical analyses were compared.

MATERIALS AND METHODS

Apple Samples

Apples were provided by Agroscope, Federal Research Station Wädens-wil (Switzerland). All the apples were of standard commercial size and colorfor the Swiss market (category 1). In total, six apple cultivars were selectedaccording to market needs and investigated between November 2002 andMarch 2003. Three cultivars were tested twice, so that the following orderresulted: Ariwa, Elstar, Jonagold, Gala, Topaz, Golden Delicious, Jonagold2,

315CONSUMER EVALUATION OF APPLE FRESHNESS

Gala2 and Elstar2. The apples were stored at 10C and at ambient relative airhumidity for a 2-week period in a room adjacent to the museum. They werestored either in plastic bags or in nets in order to induce differences in watercontent and to consequently amplify variations in sensory properties. Theapples were tested daily by consumers, alternatively from plastic bags andfrom nets during a two-week period (week 1: day 1 to day 6; week 2: day 8 today 13). The apples were in parallel subjected to descriptive sensory andphysico-chemical analyses at the beginning (day 1) and the end of the 2-weekperiod (day 10).

Consumer Test

The consumer test consisted of a questionnaire presented on a computerscreen and set up within the framework of a public exhibition on food entitled“Food Design.” Details of the test methodology are given in Péneau et al.(2006). Data on consumption of apples, age and gender were collected. Par-ticipants were asked to bite into a whole apple and to rate their liking of thesample. Furthermore, they were asked to rate the freshness, crispness, juici-ness, mealiness, sweetness, sourness and aroma (in this order) of the applesample. Although consumers were asked to rate the aroma of apples, it is likelythat they instead evaluated the overall flavor. The meaning of this term isindeed not always clear to consumers. Five-point scales were used, and eachpoint was labeled with a number from 1 to 5. Anchor points were additionallypresented with verbal labels. A total of 4,758 consumer data sets could be usedfor evaluation.

Analytical Sensory Test

Descriptive tests were carried out with a panel of 12 panelists who hadbeen recruited from the staff of the Institute of Food Science and Nutrition.They were selected on the basis of their previous experience in apple descrip-tion, their availability, as well as their willingness to participate. The panelistswere trained in the evaluation of apples and in the use of the attributes. Theattributes were previously selected by the experimenter to match the onesevaluated by the consumer panel, and they were evaluated in the followingorder: crispness, firmness, juiciness, mealiness, sweetness, sourness and flavor.Attribute intensity was scored on a 100-unit line scale (10-cm long), rangingfrom “not at all” to “very” and presented on a computer screen using the FIZZsoftware (Version 2.00 E, Biosystèmes, Courternon, France).

In each session, each panelist was presented with a set of four applesegments presented in random order: a dummy sample, one segment of anapple that had been stored in a plastic bag, one segment of an apple that hadbeen stored in a net, and, as repetition, a second segment of the apple stored


either in the plastic bag or in the net. Segments were cut out of apples, ifpossible to include both the sun-exposed and the shaded portion of the apple.They were further peeled and cored. Red overhead lighting was used to preventpossible influence of apple flesh color on ratings. The panelists were asked torinse their mouth with water between samples, and a resting time of 1 min wasimposed between samples. One sensory session per week was conducted forthe purpose of the study, but a supplementary session on apple evaluation wasorganized each week in order to maintain the panelists’ training.

Physico-chemical Measurements

The remaining parts of the 12 apples used for sensory evaluation werefurther used to measure instrumental firmness, juice release, soluble solidscontent and titratable acidity.

Of each of the 12 apples, two samples located on either side of thesegment cut out for sensory evaluation were tested for instrumental firmness.A 15-mm core borer was used to vertically remove two cylinders of flesh. Eachcylinder was placed in a sample holder, and a 10-mm-long cylinder was cut.One cylinder at a time was centered on the fixed aluminium lower plate of theuniversal testing machine (Zwick, GmbH and Co., Ulm, Germany) and com-pressed with a stainless steel upper plate (40 mm diameter) at a crossheadspeed of 50 mm/min. The compression force required to deform the cylinderto 50% was recorded (total 24 readings).

Juice release was determined gravimetrically during compressionaccording to Lapsley (1989). The cylinders used for uniaxial compressionwere preweighed using a digital balance (PR 1203, d = 0.001 g, MettlerToledo, Greifensee, Switzerland) and then placed on 1.3-mm-thick chroma-tography filter paper (Schleicher and Schüll 2727, Kassel, Germany). Juicereleased during compression was absorbed by the filter paper. The residue wascarefully removed and reweighed. Difference of weight corresponded to theamount of juice released from the apple sample during compression (total 24readings).

Two samples of juices were squeezed out of flesh from the opposite sideof the apple segments used for sensory evaluation, again including both thesun-exposed and shaded portion of the apple. Juice was placed onto a digitalrefractometer (RFM340, Bellingham & Stanley Ltd., Tunbridge Wells, U.K.)for measurement of soluble solids content, expressed in °Brix (total 24readings).

The remaining parts of the 12 apples were peeled, cored and frozen at-20C for the subsequent measurement of titratable acidity. For this analysis,apples were defrosted and reduced to one batch of juice. Acid content wasdetermined by titrating two samples of 25 mL of juice with 0.1 M NaOH


(Titrisol, Merck AG, Dietikon, Swizerland) to pH 8.1 (pH Meter 691,Metrohm, Herisau, Switzerland) according to the Association of OfficialAnalytical Chemists norm (AOAC 1984) (total 2 readings).

Data Analysis

Data analysis was carried out using SPSS for Windows (Release 12.0.1.,SPSS Inc., Chicago, IL). Statistical significance was defined at P < 0.05. Totest differences in the consumer rating of freshness, the liking and the evalu-ation of apple sensory characteristics, a three-way analysis of variance(ANOVA), using cultivar, week of test and type of packaging as main factors,was performed. Differences in sensory characteristics of the apple sampleswere tested with a mixed model ANOVA, taking panelists as the random factorand cultivar, week of test and type of packaging as fixed factors, for eachattribute. Differences between apple samples according to physico-chemicalcharacteristics were investigated with a three-way ANOVA using cultivar,week of test and type of packaging as main factors. For all ANOVAs, two-wayinteractions were considered, and nonsignificant interaction terms wereremoved from the model. For each level of cultivar and type of packaging,group means were compared for the two different storage times using Tukey’spost hoc test.

Principal component regression (PCR) was used to investigate factorspredicting freshness. This method was chosen as it allows coping with multi-collinearity problems in multivariate calibration (Martens and Næs 1989).Consumer, panel and physico-chemical data were averaged over cultivar, weekof test and type of packaging. Consumer and panel data were subjected toprincipal component analysis (PCA) of the covariance matrix, while physico-chemical data were subjected to PCA of the correlation matrix. For each dataset, linear regression was carried out, with freshness rated by consumers as thedependent variable and principal components (PCs) as the independent vari-able. Only significant PCs were considered. Regression coefficients werefurther calculated using attribute scores of the PCA. Loading factors evaluatedby consumers and the panel were standardized. The same procedure was usedfor the evaluation of the attributes influencing liking. To test the influence ofage, gender and consumption of apple on perceived freshness, consumer, paneland physico-chemical data sets were extended on the basis of these consumercharacteristics. PCA was conducted for each group on the extended data set,and the PCs were extracted. ANOVA, with freshness as the dependent variableand the PCs as covariates, was calculated for each data set. Interactionsbetween the consumer characteristics (age, gender, consumption of apple) andthe PCs were considered. Regression coefficients were further calculated usingattribute scores of the PCA.


To measure the linear relationship between consumer rating of freshnessand liking, Pearson correlation coefficients were calculated on the whole dataset. Pearson correlation coefficients based on averaged data (according tocultivar, week of test and packaging) were calculated to test the relationshipbetween firmness measured instrumentally, firmness and crispness rated by thepanel as well as crispness rated by consumers.

RESULTS

Consumer Evaluation of Apples

Mean values of liking and sensory attributes for the different cultivars andtypes of packaging and according to the week of test are presented in Table 1.Means for each week are presented because cultivar ¥ week interactions werefound for some of the attributes tested.

Evaluation of Freshness. The three-way ANOVA on freshness ratingsof apples show a significant effect of cultivar (P < 0.001) and of the week oftest (P < 0.001), but no effect of the type of packaging. In general, Jonagold2,Jonagold and Topaz were the cultivars perceived as the freshest, while GoldenDelicious, Ariwa and Elstar2 were perceived as the least fresh. Variation ofcultivar and time of storage, therefore, influenced the perceived freshness ofapples. The cultivar ¥ week interaction was not significant, suggesting that allthe cultivars decreased in freshness at a comparable rate over the 2-weekperiod of storage.

Liking and Evaluation of Sensory Characteristics. Results of thethree-way ANOVA on liking and sensory rating of apples showed a highlysignificant effect of cultivar for liking and for the six sensory attributes(P < 0.001). These sensory aspects reflect the known characteristics of applecultivars as described in a pomology review (Kellerhals et al. 2003). The effectof the week of test was investigated and showed a highly significant effect forcrispness, juiciness, mealiness and sourness (P < 0.001), and less significantfor sweetness and liking (P < 0.01). No effect was found for aroma. The appleswere perceived to be less crisp, less juicy and less sour, but sweeter and mealierduring the second week of test. Consumers also liked the apples less after thisstorage period. Finally, the type of packaging had a significant effect onjuiciness (P < 0.01) and on aroma (P < 0.05). The apples stored in plastic bagswere juicier but had less aroma than the apples stored in nets. Other sensorycharacteristics evaluated by consumers were not influenced by the conditionsof storage. A significant cultivar ¥ week interaction was also found for


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crispness (P < 0.001), indicating that some cultivars tolerated storage betterthan others respective to this characteristic.

Descriptive Analysis of Apples by the Sensory Panel

Mean values of the sensory attributes for different cultivars and types ofpackaging are presented in Table 2 for each week of test. The mixed modelANOVA on the descriptive analysis of apples by the sensory panel showed thatthere was a highly significant effect of the panel for all sensory attributesevaluated (P < 0.001). A highly significant effect of cultivar for all sensoryattributes (P < 0.001), except flavor, was also found. The effect of the week oftest was investigated and showed significant differences for firmness, crispness(P < 0.001), mealiness (P < 0.01) and juiciness (P < 0.05). No effect wasfound for sweetness, sourness and flavor. Finally, there was no significanteffect of the type of packaging on the attributes assessed, with the exception ofjuiciness (P < 0.01). In this case, apples were perceived to be juicier whenstored in nets than when stored in plastic bags. There was a cultivar ¥ weekinteraction (P < 0.01) for firmness, crispness and sourness, indicating that thetime of storage did not affect these cultivar characteristics in the same way.

Physico-chemical Characteristics of Apple Samples

Mean values of the physico-chemical characteristics for the differentcultivars and types of packaging are presented in Table 3 for each week of test.As expected, the ANOVA showed a highly significant effect of cultivar(P < 0.001) on all the physico-chemical characteristics. Analysis also revealedthat the apples decreased in instrumental firmness, juice release and titratableacidity (P < 0.001) with time of storage. The apples stored in nets showedlower juice release, instrumental firmness and titratable acidity than the onesstored in plastic bags (P < 0.01). A cultivar ¥ week interaction was observedfor instrumental firmness, soluble solids (P < 0.001) and juice release(P < 0.01), and a cultivar ¥ packaging interaction was found for instrumentalfirmness, juice release and titratable acidity (P < 0.001) as well as for solublesolids (P < 0.05). However, in all cases, the size of the effect was rather smallcompared with the main effect. Finally, a week ¥ packaging interaction wasobserved for juice release and titratable acidity (P < 0.05), suggesting thatstorage affected apples stored in bags and nets differently.

Relationship between Consumer-perceived Freshnessand Characteristics of the Apples

Characteristics Contributing to Freshness. To identify which applecharacteristics measured by consumers, panel and physico-chemical analyses


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influenced the freshness perceived by consumers, data were averaged overcultivar, week of test and type of packaging. Each data set corresponding toconsumer, panel and physico-chemical data was subjected to PCA, and maincomponents were extracted (Table 4). Linear regression analyses with fresh-ness as the dependent variable and PCs as the independent variable wereconducted. The two PCs of consumer data both contributed to freshness asshown by the linear regression (PC1: b = 0.195, P < 0.001, PC2: b = -0.052,P < 0.01). The first PC of panel data, which was explained to a great extent bytexture characteristics (Table 4), was also significant (b = 0.172, P < 0.001).Finally, the second PC of physico-chemical data, again mainly explained bytextural characteristics (Table 4), was shown to be significant in the regression(b = 0.161, P < 0.001).

Regression coefficients for each characteristic evaluated by consumersand the panel or measured instrumentally were further calculated and arepresented in Fig. 1. Crispness, mealiness and juiciness evaluated by consumerswere relevant predictors of freshness. Crispness and juiciness contributedpositively and mealiness contributed negatively. Sweetness, aroma and sour-ness had little influence on freshness. For the panel, high regression coefficient

TABLE 4.PERCENTAGE VARIANCE AND FACTORS LOADINGS FOR

THE PRINCIPAL COMPONENT (PC) EXTRACTED:CONSUMER, PANEL AND PHYSICO-CHEMICAL DATA

Principal components PC1 PC2

Consumer Percentage variance 53.78 31.45Crispness 0.36 -0.11Juiciness 0.17 -0.01Mealiness -0.19 0.06Sweetness -0.09 -0.05Sourness 0.11 0.26Aroma 0.09 0.20

Panel Percentage variance 54.82 32.67Crispness 13.15 1.01Firmness 12.78 1.45Juiciness 5.48 -2.72Mealiness -8.39 0.61Sweetness 2.27 -7.60Sourness -0.12 13.69Flavor 2.19 3.20

Physico-chemical Percentage variance 53.17 28.33Instrumental firmness 0.89 0.05Juice release -0.22 0.92Soluble solids 0.68 0.50Titratable acidity 0.91 -0.19


values for crispness, firmness, mealiness and juiciness indicated that they wererelevant predictors of consumer-perceived apple freshness. Crispness, firmnessand juiciness contributed positively to freshness; mealiness contributed nega-tively. Flavor and sweetness had little influence on freshness and sourness wasnot important for freshness. Finally, juice release and instrumental firmnesswere shown to predict freshness in a positive way, whereas titratable acidityand soluble solids content of apples did not contribute to freshness.

a

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FIG. 1. REGRESSION COEFFICIENTS OF ATTRIBUTES EVALUATED BY CONSUMERS (a),THE PANEL (b) AND CHARACTERISTICS MEASURED BY PHYSICO-CHEMICAL

ANALYSES (c) ON FRESHNESS RATED BY CONSUMERS


Influence of Demographic Factors and Consumption of Apples onPrediction of Freshness. As shown in Péneau et al. (2006), it is possible thatspecific groups of consumers perceive freshness in a different way. For thisreason, information on age, gender and consumption of apples was collected inthis study. The effect of age, gender and apple consumption on attributespredicting freshness was investigated with an ANOVA, taking freshness as thedependent variable and the PCs as covariates.

The effect of age on attributes predicting freshness was investigated. Alack of coherence in the answers of people belonging to the youngest (<15years) and oldest age categories (>70 years) has already been shown (Péneauet al. 2006) and results of the ANOVA supported these observations. These agegroups were consequently not considered in the analysis. New age groupswere constituted from the original ones: younger consumers (15–30 years),middle age consumers (31–50 years) and older consumers (51–70 years). Noeffect of age on the attributes predicting freshness was found, as shown bypanel or physico-chemical data. However, there was a significant differencebetween age groups for the PC1 extracted from the consumer data set(P < 0.001). Figure 2 shows that the contribution of crispness, juiciness, mea-liness and aroma to freshness tended to increase with the age of consumers. Incontrast, variations for sweetness and sourness were rather small.

An effect of gender on attributes contributing to freshness was found forconsumer (PC1: P < 0.001), panel (PC1: P < 0.001) and physico-chemical

-0.3

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Mealin

ess

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Sourn

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Crispness

Regre

ssio

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FIG. 2. REGRESSION COEFFICIENTS OF ATTRIBUTES EVALUATED BY CONSUMERS ONFRESHNESS RATED BY YOUNGER CONSUMERS (LIGHT GRAY), MIDDLE AGE

CONSUMERS (DARK GRAY) AND OLDER CONSUMERS (BLACK)


(PC2: P < 0.001) data. All sensory attributes rated by women were shown tocontribute more to freshness than when rated by men (Fig. 3).

To investigate the effect of apple consumption, consumers were sortedinto three groups: low consumers (�2 apples/week), medium consumers (3–4apples/week) and high consumers (�5 apples/week). No effect of apple con-sumption on attributes predicting freshness was found when panel or physico-chemical data were considered. However, a significant effect was shown forconsumer data between low consumers (b = -0.012, P = 0.646), medium

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FIG. 3. REGRESSION COEFFICIENTS OF ATTRIBUTES EVALUATED BY CONSUMERS (a),THE PANEL (b) AND CHARACTERISTICS MEASURED BY PHYSICO-CHEMICALANALYSES (c) ON FRESHNESS RATED BY WOMEN (LIGHT GRAY) AND MEN

(DARK GRAY)


consumers (b = -0.086, P < 0.01) and high consumers (b = -0.061, P < 0.05)for PC2 (P < 0.01). The contribution of all the attributes to freshness washigher for medium and high consumers of apples than for the low consumers.However, although significant, these differences were rather small, and it wasassumed that differences in the attributes contributing to freshness betweenthese groups were negligible.

DISCUSSION

Important Attributes for Freshness

All regressions showed a clear importance of the texture attributes ofapples for freshness but a rather low importance of flavor attributes. Crispness,firmness, juiciness and mealiness evaluated by consumers and the descriptivepanel as well as instrumental firmness and juice release were shown to beimportant. On the other hand, the statistical contribution to freshness of sweet-ness, sourness, aroma and flavor evaluated by consumers and the descriptivepanel as well as soluble solids content and titratable acidity measured bychemical analyses was rather small. Therefore, texture is an essential aspect ofapple freshness. The importance of texture attributes for freshness had alsobeen shown in the study of Fillion and Kilcast (2000), where subjects wereasked to give a spontaneous definition of freshness or to give three attributesthat were best associated with fresh fruits and vegetables in their opinion. Theconclusions of these authors were that the attributes most often used todescribe the freshness of fruits and vegetables were texture-related, withcrispness, crunchiness and firmness being by far the most often cited. Simi-larly, in the first part of the study reported in Péneau et al. (2006), consumerswere asked to rate the importance of different factors for freshness, and it wasshown that crispness and juiciness were the second and third most importantattributes for consumers. These results support the assumption of Bourne(2002) that the freshness of a product is frequently measured by texturalproperties such as firmness. Also of interest, Szczesniak and Ilker (1988)revealed that the three words and sensations most frequently mentioned inassociation with crispness were “fresh,” “crunchy” and “crackly,” suggesting aclose mental association between these words.

Heiss (1986) suggested a close relationship between the hedonic aspectsand the freshness of food, with “fresh” being equivalent to good, healthy ornatural while “industrially treated” would correspond to an inferior value,denatured or artificial. In our study, consumer ratings of freshness and likingwere shown to correlate (r = 0.364, P < 0.001) as calculated from the 4,758consumer data points. However, results of the linear regression with liking as


the dependent variable and PCs extracted from the PCA of consumer data asthe independent variable showed that all six sensory attributes contributed in asimilar degree to liking of apples (data not shown). Therefore, freshness andliking are influenced by different sets of attributes, and it is likely that there areimportant variables other than hedonic ones that influence consumer percep-tion of freshness.

Texture, particularly firmness, is often used as an indicator of maturity,ripeness and quality in apples (Abbott 1994). Ripening implies a change inthe strength of the structural framework of the fruit’s flesh, resulting in achange in perceived fruit texture (De Belie et al. 2000). A decrease in texturequality can therefore be an indication of apple aging (Park and Choi 2001;Link et al. 2004). If we consider that aging is mainly responsible for thechanges in the texture of a product and that texture influences the perceptionof freshness as shown in this study, we can then hypothesize that the per-ception of freshness is an assessment of the aging of a product by judgmentof its texture.

Aging has been shown in several studies to be particularly important forproduct freshness. Among 1,081 consumers interviewed on their attitude tofood labeling, 43% declared that “fresh” referred to the age of the food (MAFF2000). This perception supports the first definition of the Duden Germandictionary (Duden 1999) for the word “frisch” (fresh), with “nicht alt, abge-standen, welk” (not old, stale, limp) clearly showing an association with theage of the product. In addition to this, Schwerdtfeger (1979) argues that anydeterioration or decline of tissue from a freshly harvested state can be consid-ered a decline in freshness. In fact, the constituents of foods discussed asindicators of freshness in the introductory part are also indicators of productmodification with age.

Flavor attributes also undergo modifications during apple aging.However, it is hypothesized that decreased flavor quality may have movedconsumer attention towards texture when evaluating freshness. It has beenindeed shown that screening to optimize one sensory characteristic oftenresults in serious quality losses in other characteristics, and in particular flavorhas often been sacrificed for texture (McDaniel 1995). In addition, new storagetechnologies, such as controlled atmosphere, have also been shown to impairthe development of flavor in fruits (Mattheis and Fellman 1999). These newmethods of screening or storage might therefore have an impact on flavor,whereas texture quality remains at a good level or is even improved. Shewfelt(1999) concludes that while most consumers cite flavor as an overridingconsideration when asked how they evaluate fresh fruits or vegetables, testssuggest that consumers are much more sensitive to subtle differences in texturethan flavor and therefore tend to use texture as the primary limiting factor foracceptability.


Influence of Demographic Characteristics and Consumption ofApples on Perception of Freshness

The concept of freshness is broad and the word “fresh” might be inter-preted in different ways by consumers with different demographic character-istics and consumption habits. When the influence of age is considered, thecontribution of crispness, juiciness, mealiness and aroma on freshness mea-sured by consumers was superior for the middle age category (31–50 years)and the older age category (51–70 years) compared with that of the youngerage category (15–30 years) (Fig. 2). One could hypothesize that older peoplepay more attention to sensory attributes than younger people, who would bemore concerned about other aspects that are not intrinsic to the product andthat have not been tested in this study. However, as higher regression coeffi-cients are observed for most of the attributes evaluated, it is reasonable to thinkthat these discrepancies are due more to larger variations in answers withinsome age groups rather than to a real difference in perception of freshness.Younger participants could vary more in their sensory ratings than olderparticipants, leading to lower regression coefficients. Similarly, it was shownin Péneau et al. (2006) that when asked about the importance of attributes forfreshness, consumers of different ages did not differ in their ratings of taste,crispness, juiciness and storage time. However, they differed in the importancegiven to appearance, organic and nutritional value. Although it is not possibleto draw clear conclusions, it is suggested that people belonging to different agecategories accord similar importance to sensory attributes for the evaluation offreshness, whereas they differ in the importance given to nonsensory attributessuch as organic and nutritional value.

Looking at the effect of gender, consumer, panel and physico-chemicaldata showed a higher contribution of all attributes to the perception of fresh-ness in the case of women than in the case of men (Fig. 3). A first interpretationof this result is that, as for the age category, there is a larger variation in theratings of men compared with those of women. When panelists’ sensoryratings are considered, Nicod (1998) stated that women performed better thanmen, regardless of age. This observation might also be true with regard toconsumers. A second interpretation of this result might be that generallywomen accord more importance to sensory attributes for freshness than men.It was found, that in the evaluation of the freshness of apples, women gavehigher ratings of importance for taste, crispness and juiciness than men(Péneau et al. 2006). It is conceivable that men’s perception of freshness isdriven by other characteristics than the ones studied. As men are generally lessinterested in food-related topics than women (Worsley and Scott 2000), it isalso possible that their understanding of the concept of freshness is less clearand that they therefore give less importance to the attributes considered.


The influence of apple consumption on the perception of freshness wasnegligible. Differences for taste, crispness and storage time between consum-ers having different level of apple consumption were not found in the first partof this study, although they differed in the importance given to appearance,nutritional value and organic (Péneau et al. 2006). Therefore, consumers withdifferent levels of apple consumption seem to give the same importance tosensory attributes influencing the perception of freshness (i.e., taste, crispness,juiciness) but differ in the importance given to nonsensory attributes (i.e.,organic, nutritional value).

In conclusion, sensory attributes of importance for perceived freshnessare independent of the age of consumers and of the quantity of apples eaten perweek. On the other hand, although the influence of gender on perceivedfreshness has not yet been clearly elucidated, it seems that women give moreimportance to sensory attributes than men do.

Comparison of Consumer, Panel and Physico-chemical Data for thePrediction of Freshness

The prediction of freshness by characteristics assessed by consumers, bythe sensory panel, and as measured by physico-chemical analyses were com-parable (Fig. 1). Crispness, mealiness and juiciness were found to be importantfor freshness when assessed by consumers. The same attributes were importantwhen assessed by the sensory panel, with the addition of firmness. Finally,juice release and instrumental firmness measured by physical analyses wereshown to be of importance for freshness. In all cases, flavor attributes contrib-uted to a limited extent to freshness.

The consumers differed from the sensory panel in that their rating ofsweetness contributed negatively to freshness, whereas the contribution ofsweetness was positive when assessed by the sensory panel (Fig. 1). Overall,however, the contribution of attributes for the prediction of freshness asassessed by consumers and by the sensory panel was very similar. This is aninteresting result as methodologies of sensory evaluation for consumers andthe panel exhibited a number of differences. Consumers were given a wholeapple while panelists were given one segment of a peeled and cored apple.Daillant-Spinnler et al. (1996) also showed small differences in the sensoryevaluation of unpeeled half-apples and peeled quartered apples. Consumerstested only one apple, in contrast to the panelists, who tested four samples. Thetype of scale used for the apple evaluation differed between consumers(5-point scale) and panel (100-unit line scale), and the attributes rated by thesensory panel were defined during training whereas this was not the case forconsumers. Consumers were inexperienced with this type of task and notunder optimal conditions for testing. It is more than likely that the large data


set compensated for individual differences between consumers because of thelack of training. Nevertheless, consumers were assumed to be familiar enoughwith apples to assess them in a reliable way: Swiss consumers are known toconsume large amount of apples (SOV 2003).

Juice release measured instrumentally and juiciness evaluated by con-sumers and the panel contributed similarly to freshness. This result suggeststhat these three methods of measurement for juiciness were effective in assess-ing characteristics that influence apple freshness (Fig. 1). On the other hand,instrumental firmness contributed less to freshness than firmness evaluated byconsumers and panelists. It can be hypothesized that although firmness mea-sured instrumentally is very highly correlated to sensory evaluation of firmnessand crispness by the panel (r = 0.899, P < 0.001 and r = 0.836, P < 0.001,respectively) and highly correlated to consumer evaluation of crispness(r = 0.765, P < 0.001), the characteristics measured differ to some extent.Several authors are aware of this fact and advise that a combination of severalvariables from a multivariate mechanical measurement be used instead of asingle-variable test for predicting texture sensory attributes (Abbott et al.1984).

These results suggest that all three methods, namely, consumer tests,sensory panel and physico-chemical measurements, would be effective forevaluating attributes contributing to freshness. Regression coefficient valuesobtained from consumer data were generally higher than those obtained frompanel and physico-chemical data. This might be due to the high number ofparticipants. Therefore, consumer perception of freshness was better predictedby consumer assessment of sensory characteristics.

CONCLUSIONS

This study has shown that texture attributes are of particular importancefor the evaluation of apple freshness. As change of textural properties accom-panies aging of the apple, the evaluation of the freshness of an apple corre-sponds to the measurement of its age by evaluating its textural quality.

The relative importance of texture as a quality attribute varies amongtypes of fruits and is higher for firm, fleshy fruits such as apples and pears(Brennan et al. 1977). It is therefore hypothesized that attributes other thantextural ones are important for the evaluation of freshness of other types offruits.

Consumer and panel evaluation as well as physico-chemical measure-ments agreed regarding the prediction of freshness. Generally, consumer per-ception of freshness of apples was better predicted by consumer assessment of


sensory characteristics. In a classical set-up, sensory evaluation of the productsby a trained sensory panel is likely to be the best approach to take forpredicting freshness.

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RELATING CONSUMER EVALUATION OF APPLE FRESHNESS TO … · RELATING CONSUMER EVALUATION OF APPLE FRESHNESS TO SENSORY AND PHYSICO-CHEMICAL MEASUREMENTS S. PÉNEAU 1, P.B. BROCKHOFF2,