Influence of packing materials and temperature on yeast ... 4_Amariei-Gut...biomass composition and on growth rate. The yeast Saccharomyces cerevisiae belongs to the mesophyll group,

Romanian Biotechnological Letters Vol. 19, No. 4, 2014 Copyright © 2014 University of Bucharest Printed in Romania. All rights reserved

ORIGINAL PAPER

9475 Romanian Biotechnological Letters, Vol. 19, No. 4, 2014

Influence of packing materials and temperature on yeast activity

Received for publication, February 20, 2014 Accepted, June20, 2014

SONIA AMARIEI*, SORINA ROPCIUC*, GHEORGHE GUTT, MIRCEA OROIANFaculty of Food Engineering, “Stefan cel Mare” University of Suceava, Romania*Address correspondence to: “Stefan cel Mare” University of Suceava, Faculty of Food Engineering, 13 Universitatii Street, 720229, Suceava, Romania. Tel.: +40230216147; Fax: +40230523267; Email: [email protected], [email protected]

Abstract

A commercial form of baking yeast Saccharomyces cerevisiae, was analyzed in terms of the influence of temperature and packing materials during storage. Yeast activity at different temperatures, from +3 ± -3 ºC, 22-24°C and up to 30°C over a period of 50 days was determined. As packing materials there have been studied: polyethylene, cellophane, OPP (oriented polypropylene) and aluminum, materials that can influence the fermentation activity of the yeast during storage. Results obtained showed that yeast stored at low temperatures (0-10ºC) mantains the best yeast fermentative activity. A strongly significant correlation between the variables of fermentative activity and packing material with the correlation coefficient r = 0.996 is observed at individually packed yeast (cellophane foil). Packing materials have been analyzed in terms of water absorption, thickness and specific mass. Statistical correlations calculated by the Pearson matrix between the variables of yeast activity and packing material indicate that the cellophane mantains the fermentative activity at its best value (r = 0.996).

Keywords:Saccharomyces cerevisiae, packing materials, fermentative activity.

1. Introduction

Physical and chemical transformations of packed foods, the processes that occur throughout the entire period from packing to consumption are: solidification by drying, crystallization, formation of hydrates, autooxidation, non-enzymatic browning reactions, enzymatic transformations. These transformations that generate changes in organoleptic and toxicological aspect are closely related to packing and materials characteristics used in their manufacture. In commerce yeast can be found in several different forms: compressed yeast (fresh), active dry yeast, protected active dry yeast and instant dry yeast. Choosing a specific commercial form of yeast in order to obtain a quality bread is done by taking into consideration the quality of the yeast. In order to obtain the biomass extremely useful in backing industry, the yeast Saccharomyces cerevisiae is grown on carefully selected environments with the help of a complex of physical-chemical, biochemical, microbiological and thermoenergetic processes (1).

The nutritional requirements of baking yeast are: carbohydrates, nitrogen, phosphorous, minerals, bio-stimulating substances, temperature of 30...35°C, the pH in the weakly acidic range and the absence of contamination substances. The yeast Saccharomyces cerevisiae is capable of fermenting even under anaerobic conditions but with an excess of fermentable carbohydrates (1-3). All strains of Saccharomyces cerevisiae can metabolize glucose, maltose and trehalose.


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Among extrinsic factors, temperature is one of the important physical parameters in the optimization of the process. Changes in temperature affect the yield of conversion of the substrate into the desired product, on the nutritional requirements of yeast, on obtained biomass composition and on growth rate.

The yeast Saccharomyces cerevisiae belongs to the mesophyll group, the optimum temperature is between 26ºC and 36ºC. At a temperature higher than 40°C, baking yeast does not multiply, and therefore the movement with a few degrees around the optimum of growth temperature not only affects the yield in resulted biomass and growth rate, but also the biochemical composition of yeast cell.

Yeast cells can withstand very low temperatures to near absolute zero, surviving cold easily in a dry than in a wet environment. From experiments, it was observed that by lowering the temperature below 0°C there is a reduction in the rate of metabolism. A decrease with 10ºC under the minimum temperature (-3°C) leads to a 50% decreasing in the rate of metabolism of nutrients, due to the folding of protein chains and masking active centers of enzymes so that they do not connect with the substrate and do not function as biocatalysts. At low temperatures, yeast losses intracellular water, and go into dormant life when metabolism is very slow, remaining viable for a long time (4-7).

Water is important for yeast cell not only because it is the main constituent in quantitative terms, but it also represents about 80% of the living cell. It performs the functions of solvent for intracellular metabolites, maintaining cell shape and size. Yeast requires for normal growth an amount of free water to ensure a good transfer of nutrients into the cell.

Aeration of the environment is important to provide continuously the yeast cell with oxygen, to remove the formed carbon dioxide that has an inhibitory effect on the process of reproduction, fast transport to the cells of added nutrients and maintainance of cells in a state of suspension.

2. Materials and methods The purpose of this study is to determine through physico-chemical analyses the yeast

behavior in various types of packing materials throughout the validity term and the temperature influence during storage.

For the determination it was taken a sample of compressed yeast resulted from the same batch with different grammage and packed in different materials. Thus, the following yeast samples were taken for analysis:

- 0.5 kg yeast package, individually wrapped in OPP foil and then paraffin paper, stored in 10 kg carton boxes;

- 0.5 kg yeast package, individually wrapped in sufite paper and then wrapped 5 pieces each in cellophane foil, forming 2.5 kg packets;

- 0.5 kg yeast package, individually wrapped in sulfit paper and polyethylene foil, stored in 10 kg carton boxes;

- 0.025 kg yeast package, wrapped in aluminum foil, waxed on the inside, then wrapped 8 packets in cellophane foil, with a weight of 2.4 kg.

Physicochemical analyses were performed on the individually and in boxes wrapped yeast packages, with the amount of 10 kg, at different time intervals starting with the packing moment and up to 50 days from packing, thus determining the yeast activity and yeast cell vitality.

SONIA AMARIEI, SORINA ROPCIUC, GHEORGHE GUTT, MIRCEA OROIAN


Yeast samples were analyzed also in terms of behavior at different temperatures: +3 ± -3ºC, 22-24ºC and 30ºC at the age of 0, 7, 14, 28, 36 and 50 days.

The method of analysis used to determine the capacity of the yeast leavening fermentation after an hour, respectivelly two hours after the packaging was removed is done with a fermentograph. By reading fermentograms, fermentation capacity can be appreciated, known as yeast activity that is the total amount of released carbon dioxide, and also the duration of its fermentation, i.e. the time in which is obtained the optimum of the fermentation. The result was expressed in mg CO2/l. The influence of packing material on the capacity of yeast fermentation and the outer packaging of packaged yeast were studied. Also the influence of the packaging position, indoor, outdoor, in a row, centrum was the subject of determinations.

The analyzed samples consisted of packets from the box, Cext and Cint, i.e. an external package and a package inside the string respectively, usually the third package in the range of five packages; in the packages in the outer cellophane, Text and Tint, with the same meanings as those from the box.

Analyses were performed every four days in the case of the samples stored at temperatures above 22-24°C, respectively 30°C due to high temperature and rapid changes. In the case of the samples stored at +3 ± -3°C the analyses were performed once a week due to optimum storage conditions.

3. Results and discussions

The thermal regime applied to compressed yeast during storage and transport period

influences its conservability. Refrigeration leads to slowing down metabolic processes and the extension of shelf life. Packing materials were analyzed in terms of water permeability, water absorption, specific weight and thickness as in Table 1. Table 1. Characteristics of packing materials

Material Water permeability Water absorption 24h

%

Specific weight2g/m

Thickness

m

OPP very low 0.006 – 0.3 17 ± 2 20 ± 2

Cellophane high 19 33.5 23.3

Polyethylene impermeable < 0.015 21.6 -

Paraffin paper impermeable - 53.2 ± 5 55 ± 5

Paraffined

aluminum paper

impermeable - 69 65 ± 5

The data on packing materials reveals different features presented by the four types of packing. Regarding the water absorption, cellophane has the highest value of 19% by comparison with the other materials that are impermeable or with a very low permeability. This property of cellophane can provide breathing of yeast, and facilitate the removal of water from the



product, helping the same time to the maintaining the vital functions for a longer period of time. Critical fermentative activity is recorded according to graphic expression in individual packages wrapped in OPP. The activity at every two hours at a temperature of 30°C and the yeast age for 12 days (V12 (30)) is of 48 mg CO2, the yeast vitality indicates the lowest value. The best fermentative activity stands in packages inside the box (1250 mg CO2).

Table 2.Yeast fermentative activity in OPP packing

Results V0(3)

V7(3)

V14(3)

V21(3)

V28(3)

V36(3)

V50(3)

V0(22)

V5(22)

V9(22)

V13(22)

V0(30)

V4(30)

V8(30)

V12(30)

V12(30)

Act1_OPPCext 780 800 750 760 760 730 700 780 730 530 240 780 650 130 - 100

Act1_OPPCint 780 770 760 730 730 720 690 780 710 680 190 780 510 100 - 120

Act1_OPP.pac 780 780 750 740 720 750 660

1200 760 600 300 780 730 270 49 250

Act2_OPPext

1200

1100

1130

1150

1150

1140

1100

1200

1110 890 440

1200

1080 - - 230

Act2_OPPint

1200

1250

1220

1150

1060

1100

1040

1200

1160

1060 -

1200 890 - - 48

Act2_OPPpac

1200

1200

1170

1190

1120

1150

1050

1200

1200

1000 520

1200

1200 620 - -

Cext = package outside the box;

Cint = package inside the box (the third in a row of five packs);

ext = package outside the foil;

int = package inside the foil (the third in a row of five packs);

pac. = individual yeast package, stored at the studied temperature.

Table 3. Yeast fermentative activity in cellophane

Results V0(

3) V7(

3) V14

(3) V21

(3) V28

(3) V36

(3) V50

(3) V0(22)

V5(22)

V9(22)

V13(22)

V17(22)

V0(30)

V4(30)

V8(30)

V23(22)

Act1_CE.Cext 780 770 770 770 770 740 700 780 770 730 440 420 780 750 390 110

Act1_CE.Cint 780 760 760 740 730 700 720 780 770 460 440 420 780 770 430 110

Act1_CE.Text 780 770 770 780 760 740 800 780 810 800 700 380 780 800 760 -

Act1_CE.Tint 780 750 800 770 750 760 760 780 810 790 700 370 780 800 740 -

Act1_CE.P.pac 780 800 800 780 800 800 770 780 880 750 440 70 780 850 590 -

Act2_CE.Cext

1200

1250

1200

1230

1200

1100

1100

1200

1210

1200 740 660

1200

1230 720 -

Act2_CE.Cint

1200

1160

1170

1130

1150

1050

1140

1200

1200 820 770 690

1200

1250 740 -

Act2_CE.Text

1200

1150

1200

1200

1150

1110

1200

1200

1210

1230 1130 670

1200

1270

1210 -

Act2_CE.Tint

1200

1200

1240

1150

1150

1150

1090

1200

1240

1250 1140 700

1200

1240

1190 -



Act2_CEpPpac

1200

1190

1210

1200

1150

1200

1160

1200

1300

1200 700 -

1200

1250 970 -

The yeast activity by using cellophane as packing material indicates the highest fermentative activity in yeast aged 5 days at 22°C (1210 mg CO2). The lowest fermentative activity was recorded at 23 days after production and stored at 22°C in individual packages (V23(22)).

Table 4. Yeast fermentative activity in polyethylene

Results V0 (3)

V7 (3)

V14(3)

V21(3)

V28(3)

V36(3)

V50(3)

V0 (22)

V5 (22)

V9 (22)

V13 (22)

V17 (22)

V0 (30)

V4 (30)

V8 (30)

V12 (30)

Act1_PECext 780 770 760 720 730 720 690 780 730 350 100 - 780 660 200 - Act1_PE.Cint 780 760 750 720 740 720 750 780 650 280 100 - 780 500 190 - Act1_PE Ppac 780 750 750 730 760 730 680 780 760 600 330 110 780 710 300 100 Act2_PE.Pext

1200

1200

1180

1110

1150

1050

1040

1200

1180 630 - -

1200

1100 - 140

Act2_PE.P tipla

1200

1190

1190

1150

1130

1050

1100

1200

1060 - - -

1200 900 - -

Act2_PE.Ppac

1200

1150

1180

1130

1120

1060

1150

1200

1210

1000 600 -

1200

1140 560 -

The polyethylene foil as a packaging material for yeast indicates a high fermentative activity at 22°C and aged 5 days in individual packages. The lowest fermentative activity (100mg CO2) is observed in the packs wrapped 5 each in blisters with the age of 12 days and stored at a temperature of 30°C (V12 (30)). Table 5. Yeast fermentative activity in aluminum foil packaging

Results V0 (3)

V7 (3)

V14 (3)

V21 (3)

V28 (3)

V36 (3)

V50 (3)

V0 (22)

V5 (22)

V9 (22)

V13 (22)

V0 (30)

V4 (30)

V8 (30)

Act1_Al.Cext 760 750 750 720 700 720 690 760 720 470 250 760 480 50 Act1_Al.tipla 760 760 760 700 710 700 660 760 740 250 140 760 650 430 Act1_Al.pac 760 760 740 710 700 690 650 760 720 650 380 760 730 530 Act2_Al.Cext 1200 1180 1180 1150 1110 1080 1000 1200 1130 800 - 1200 830 - Act2_Al.tipla 1200 1200 1130 1150 1150 1150 950 1200 1160 - - 1200 1100 800 Act2_Al.pac 1200 1100 1180 1130 1130 1060 1000 780 1150 980 - 1200 1160 1010

Packing yeast in paraffin aluminum foil on the inside has as maximum fermentative

activity the value of 1200 mg CO2, in freshly packed yeast (V0) and storage temperature of 22°C. The lowest fermentative activity is noted at the same temperature of 22°C, but at 9, 13 and 17 days. The yeast reduces its for fermentative capacity at 30°C at 8 and 12 days of age.

Statistically analyzing the conditioning between the variables of fermentative activity, reaction to the type of packaging and the age of yeast cells by Pearson correlation matrix (table 6), it is concluded that the best activity in yeast fermentation is mantained in the case of cellophane wrapped yeast, stored in cardboard boxes. The calculated Person correlation coefficient has the value r=0.998 in the yeast packages inside the box (CEint). A very high



significant correlation between the variables of fermentative activity and packing material with correlation coefficient r = 0.996 is observed in individually wrapped yeast (CEpac).

In polypropylene packing the Pearson correlation coefficient indicates a strongly significant correlation between the fermentative activity and packing. r = 0.995.

Polyethylene and aluminum foil ensures the maintenance of the fermentative activity at average values, but one cannot notice a very high significant correlation for these types of packing material

Table 6. Pearson correlation matrix between the variables fermentative activity in different packings and yeast age.

The graphic representation of the Pearson correlation matrix (Figure 1) groups together the yeast activity in terms of variable ties intensity. Thus, in dial 1, counterclockwise, Act 1 of yeast in cellophane pack together with groups from Act1 of yeast packed in aluminum. At the intersection of dial 1 with dial 2 is noticeable the yeast activity in polyethylene packing, fact that indicates an proximity of the values of these two types of packing. Dials 2 and 3 contain yeast activity groups in polyethylene, polypropylene and aluminum packing. Dial 4 groups the activity at 2 hours in packages wrapped in cellophane. The analysis of the main components, the storage temperature and the age of the yeast (Figure 2 and Table 7) indicate very high significant correlations r=1.000 for fresh yeast obtained and stored at +3°C. Significant strong correlations are revealed at the age of 14, 21 and 28 days yeast stored at +3°C. Significant negative correlations are noticed when storing the yeast at 22°C



and 30°C at the age of 12 and 23 days. The calculated Person correlation coefficient indicates strongly negative correlations, r=-0.564 at the age of 12 days stored at 30°C.

Figure 1. Graphic representation of how fermentative

activity is grouped in packing

Graphic representation of fermentative activity grouped

in packing

Figure 2. Analysis of the main components; age and

storage temperature of packed yeast

As a result of the analysis, it was found that yeast stored in conditions recommended by the manufacturer, i.e. 0-10°C, it maintains the best its organoleptic and physico-chemical properties. Table 7. Hierarchical cluster analysis of fermentative activity compared to Euclidean distance

Observation 1-17 Class

Act1_CE.Cext 1

Act1_Cepac 1

Act1_Al.Cext 1

Act1_OPPCext 1

Act1_Al.pac 2

Act2_PE.ext 2

Act2_PE.tipla 3

Act 1_OPPCint 3

Act2_PE.pac 3

Act2_Al.Cext 2

Act2_Al.tipla 4

Act2_Al.pac 5



In case of hot storage, at temperatures above 30°C, the processes that occur take place fast. Thus, the lifetime of the yeast stored in OPP boxes is of only eight days, the rest having a maximum duration of twelve days.

The cluster analysis of the fermentative activity (Table 8) divides the yeast activity in five classes, the best activity is preserved in cellophane packing and weakest activity in aluminum packing.

Table 8. Pearson correlation matrix between storage temperature and yeast age

The mathematical model of the statistical relationship between the average absorbance activity and cellophane water absorption. Fermentative activity= (883.96-820)*Water absorption in 24h -19

Figure 3. Graphical representation of the mathematical model

Mathematical equation logarithmic curve

y = 760.98 ln(x) - 429.2 =1 2R

0.95 confidence interval



The mathematical model of the relationship between the fermentative activity and the quality characteristic of packing material (figure 3), calculated at the confidence level of 0.95% has as ideal absorption the cellophane type packing. The point marked on the graphic with the value of 1215.412 is the best fermentative activity performed at the studied materials, the correlation ratio of logarithmic equation r2 = 1.

4. Conclusion

The used packing materials (aluminum, OPP and polyethylene) have a very low capacity to absorb water (for aluminum the value beeing practically zero), the process stopping migrations of the cell constituents during the storage of the yeast.

This action affects yeast activity thus: most constitutive enzymes are activated, soluble minerals that provide enzymes activity are removed with the increase of the moisture. Yeast is unable to produce its own energy through sugars metabolism from the environment, and in the presence of oxygen sources, the yeast cell produces ATP (adenosine triphosphate). With the lack of oxygen and sugars sources, yeast enzymes that act as catalysts for chemical reactions are destroyed and no other reactions occur to produce energy (8- 10). Yeast endogenous substances (protein, glycogen, lipids) provide metabolic substrate for a relative time, maximum 72 hours. Baking yeast consumes its endogenous substances and autolyze due to high temperature and reduced aeration conditions because of the packing materials and improper storage conditions (temperatures above 10°C). The packing material that ensures maintaining good values of fermentative characteristics is the cellophane wrap while the optimum temperature is +3 - +10°C.

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Influence of packing materials and temperature on yeast ... 4_Amariei-Gut...biomass composition and on growth rate. The yeast Saccharomyces cerevisiae belongs to the mesophyll group,