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Bioresource Technology 57 (1996) 215-216 Copyright © 1996 Elsevier Science Limited Printed in Great Britain. All rights reserved

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Short Communication

Malt Caramel from Tubers of Cyperus esculentus

Abstract This work was done to ascertain the feasibility of obtaining caramel from malted tubers of Cyperus esculentus. The tubers of C. esculentus were partially germinated for 10 days and sun-dried for 24 h. The sun-dried samples were then kilned at 70°C for 24 h and at 120°C for 5 h for further caramelization. The kilned samples were finely crushed, infused with deio- nized water at 60°C and the malt extract heated up to 127~C, to give a brown-black syrupy substance, car- amel, with specific gravity 38.97+_0. 77 °B~. Reducing sugars as o-glucose in the unmalted tubers before and additional sugars after hydrolysis for 30 min were 24.75+4.54 and 64.80+2.28mg/g of sample, and in the green malt 123.13++_4.28 and 82.07++_4.13 mg/g of sample, respectively. Copyright © 1996 Elsevier Science Ltd.

Key words: Malt, caramel, tubers, Cyperus esculentus.

INTRODUCTION

Cyperus esculentus is a sedge of the family Cyper- aceae which produces rhizomes from the base and tubers which are somewhat spherical, with sitting diameter 5 - 1 7 m m (Lowe & Stanfield, 1974). The plant itself is merely a weed, and the sweet-tasting tubers serve only as a casual masticatory and have no other domestic or industrial uses. The tubers are rich in carbohydrates, mono-, di- and poly-sacchar- ides.

Sugar acids and reducing sugars (polyhydroxy-car- bonyl compounds) show a browning reaction (or caramelization) when heated to relatively high tem- peratures. The reaction is accelerated by the presence of carboxylic acids and their salts, phos- phates, metallic ions and nitrogenous substances present in foods (Meyer, 1982).

Caramel can be prepared from malted-cereal syr- ups, but there is no record of caramels from tubers. This paper, therefore, reports the preparation and characterization of caramel from malted tubers of Cyperus esculentus.

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METHODS

Samples of tubers Semi-dried and flesh samples of tubers were pur- chased from the local market at Awka, Anambra State of Nigeria.

Malting of the samples of Cyperus esculentus tubers The semi-dried tubers, which were dormant, were washed thoroughly and steeped in water at room temperature, 27°C, for about 24h. The steeped tubers were put into a fiat container and kept in a dark and cool compartment for the germination step of the malting process. The malt was watered until the desired germination stage was attained after 10 days. The green malt was then sun-dried for 24 h, followed by kilning at 70°C for 24 h and at 120°C for 5 h for further caramelization.

Malt extraction and caramelization The kilned malt was milled to a fine powder and 50 g of the milled malt infused with 300 ml of deio- nized water at 60°C and the malt removed as the filtrate. The malt extract was heated in an open vessel at a temperature of 127°C until a brown- black syrupy substance was obtained.

Physico-chemicai properties of the malt caramel The tinctorial power, odour and stability to alcohol were determined by the procedures described by Fetzer (1964).

The specific gravity (relative density, r.d.) was determined by the method of Williams (1966) and converted to the Baum6 scale using the relationship given by Uvarov et al. (1979): DegreeBaum6- (°B6) = 144.3(r.d.- 1)/r.d.

Estimation of reducing sugars as D-glucose Samples (20 g) of the germinated (green malt) and ungerminated tubers were finely milled, infused with 100 ml deionized water, and pressed mechanically to extract all the sugar juice. Benedict's method, as described by Bassir (1975), was then used to esti- mate the concentrations of reducing sugars as glucose before and after acid hydrolysis for 30 min.

216 Short communication

Table 1. Concentrations of reducing sugars as o-glucose in green malt and unmalted tubers of Cyperus esculentus a

Fresh Germinated ungerminated (green malt)

(unmalted) tubers tubers

Reducing sugars as D-glucose (mg/g sample)

Additional reducing sugars as D-glucose after hydrolysis (mg/g sample)

24.75 +__ 4.54 123.13 ± 4.28

64.80 __ 2.28 82.07 ± 4.13

"Values are means + SD of three analysis.

R E S U L T A N D D I S C U S S I O N

The caramel produced from the malted tubers of Cyperus esculentus appeared as a brown-black syrup. The concentrations of reducing sugars as D-glucose before and after hydrolysis in the germinated (green malt) and ungerminated samples are shown in Table 1 and the properties of the caramel are given in Table 2.

The product remained clear in 50% alcohol. It also had an amber shade, in keeping with the tincto- rial power for beverage and brewers' colours.

The specific gravity obtained fell within the standard caramel colour range of 30-40°B6 (Fetzer,

Table 2. Properties of the malt caramel from tubers of Cyperus esculentus a

Parameter Value/observation

Specific gravity 38.97 + 0.77°B6 Odour mild acrid odour Tinctorial power amber

(colour intensity) Stability to clear in 50% alcohol

alcohol Caramelization 120-127°C

temperature

"Values are mean +_ SD of three analysis.

1964), and also came within the narrower range of 36-40°B6, indicating a fair adjustment for the three important variables of solids, tinctorial power and viscosity.

Kilning at temperatures up to 120°C produced a 'special malt' (Kneen, 1967) and from this the car- amel was also obtained. Hence, the caramel should find applications where it will add body, flavour or colour, as in some bakery products, non-alcoholic malt beverages, dark beers and in condiments pro- duction. It might then be developed for other applications.

R E F E R E N C E S

Bassir, O. (1975). Handbook of Practical Biochemistry. Iba- dan University Press, Ibadan, Nigeria, pp. 25-30.

Fetzer, W. R. (1964). Caramel colour. In Kirk-Othmer Encyclopaedia of Chemical Technology, 2nd edn. John Wiley, New York, pp. 63-69.

Kneen, E. (1967). Malts and malting. In Kirk-Othmer Encyclopaedia of Chemical Technology, 2nd edn. John Wiley, New York, pp. 861-885.

Lowe, J. & Stanfield, D. P. (1974). The Flora of Nigeria Sedge (Family Cyperaceae). Ibadan University Press, Iba- dan.

Meyer, I. H. (1982). Food Chemistry. The AVI Publishing Company, Westport, Connecticut.

Uvarov, E. B., Chapman, D. R. & Isaacs, A. (1979). The Penguin Dictionary of Science, 5th edn). Penguin Books, Harmondsworth, Middlesex, UK.

Williams, K. A. (1966). Oils, Fats and Fatty Foods, 4th edn. Elsevier, New York, pp. 88-122.

S. C. Umerie & J. N. Enebeli

Department of Science Technology, Nnamdi Azikiwe University, P.M.B. 5025, Awka, Nigeria

(Received 17 October 1995; revised version received 20 May 1996; accepted 25 May 1996)