The Effect of Controlled Storage Conditions on ...

The proceeding of the 8'hISB:647-652(2001)

The Effect of Controlled Storage Conditions on Changes of Selected Components of Buckwheat R. Przybylski, L. Malcolmson11, G. Mazza2), and N. A. M. Eskin University of Manitoba, Department of Foods and Nutrition, Winnipeg, Manitoba, Canada IlCanadian International Grain Institute Winnipeg, Manitoba, Canada 2lFood Research Program Agriculture and Agri-Food Canada Pacific Agri-Food Research Centre Summerland, BC, Canada

INTRODUCTION Buckwheat (Fagopyrum esculenturn Moench) is a cool climate plant of the Polygonaceae family cultivated for food and (Marshall and Pomeranz 1982; Mazza 1993). In North America, buckwheat is used primarily for making buckwheat pancakes, and is marketed in the form of prepared mixes. Buckwheat is also used with vegetables and spices in kasha and soup mixes, and with wheat, corn or rice in ready-to-eat breakfast products, porridge, bread and pasta products. In Japan, buckwheat flour is used primarily for making soba or sobakiri (buckwheat noodles) and Teuchi Soba, hand-made buckwheat noodles. An extruded ready-to-eat cornbuckwheat breakfast product of high nutritional value is being produced and marketed in western Europe, this product contains 14% protein and 8% soluble fiber (Mazza et al1999). The main buckwheat quality attributes are colour and flavour of the groats (Mazza 1986, 1988, 1993, 1994). The colour of fresh buckwheat groat is light green while in old seed colour is changing to reddish brown. The flavour is characteristic for fresh buckwheat, freshly milled buckwheat, changing to bland with a rancid tone in old buckwheat. Przybylski et al. (1995) found that the content of total volatile compounds in buckwheat seeds decreased with storage in air, and the concentration of saturated and norisaturated aldehydes increased with storage time. Their also observed that milled buckwheat samples stored in air at room temperature for 15-30 min were losing 50-70% of their volatile flavour components as compared with fresh ground samples. In the present st4dy the changes of buckwheat components in buckwheat seed stored under reduced oxygen and elevated carbon dioxide levels are reported.

MATERIALS AND METHODS

Buckwheat and Storage Conditions Buckwheat (var. Mancan) grown commercially in 1995 in Morden, Manitoba area, was stored under controlled conditions. The buckwheat seed was cleaned to remove sand, weeds, small and immature seeds, then dehulled by passing the seed between a horizontally mounted stationary emery stone and an adjustable rotating stone of equal size (Campbell and Chubey 1985). Whole and dehulled seed were stored at - 400'C ± 10'C for up to 3 weeks before controlled storage. All samples were packaged in mesh bags, allowing passage of atmospheric gases, and kept in a 0.8 m.1 controlled atmosphere storage chamber under nitrogen atmosphere

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containing 1.5% of oxygen and 1.5% of carbon dioxide for up to 60 weeks. The storage temperature w~s OO°C ± 2~oC, t~e humidity during storage was held at 48% by applying a saturated solutIOn of magnesIUm filtrate. Samples were removed at 4-week intervals and stored in polyethylene bags at - 40°C, prior analysis.

Sensory Evaluation of Stored Buckwheat An eight member trained sensory panel evaluated the odour of stored buckwheat. Samples were milled using an Allis-Chalmer mill. Ten grams of milled buckwheat were placed in a 125 mL glass jar with a screw cap lid. Glass jars were placed in a water bath held at 50°C. A reference sample of milled buckwheat that had been stored at - 28 °C was provided to each panellist. Panellists rated the intensity of the reference odour, described as "grainy/cooked vegetables/ dusty", as well as the intensity of off-odour using 9 point intensity scales where 1 = none, and 9 = intense. Panellists were asked to characterize the perceived off-odours in samples analysed. Panellists evaluated four samples, took a 5 min break and then evaluated the remaining three samples. Samples were coded with three digit numbers and served in a randomized order. Panel sessions were held in a sensory panel room equipped with eight computerized booths. The software program CSA Computerized Sensory Analysis (Compusense Inc., Guelph, Canada) was used to input and record panellists' responses. Samples were evaluated under red lights to mask any possible colour differences. Analysis of Lipid Components Milled buckwheat seeds (5g) were sifted through a standard #10 sieve to remove hulls. The groats were extracted with hot butanol saturated with water at 80-90°C for 3 hours and mixed every 10 minutes. This extraction was repeated three times and extracts combined. Finally, residual groats were twice extracted with chloroform: methanol (1 :2, v/v) and separated chloroform layer combine with butanol extracts. The resulting extract was evaporated to dryness on a rotary evaporator under vacuum and nitrogen at 35°C. The residue was dissolved in chloroform: methanol (1: 1, v/v) which were used for lipid quantification. Composition of lipids was determined using thin layer chromatography with flame ionization detector (Iatroscan, TLC-FID). Lipid extracts were applied on Chromarods III at the total amount of 10-20 fig. Components were separated by development in a mixture of dich1oroethane : chloroform: acetone: acetic acid (59: 10: 1.4:0.4, v/v) for 1 hour. After development the rods were dried at 125°C for 4 minutes then run on the Iatroscan under following conditions: hydrogen and air flow 195 and 2000 mL/min, respectively. Scan speed used was 35 seconds per rod. For quantification, calibration curves for every individual analysed component were prepared and verification mixture of standards was run on one rod for every set of samples. Analysis of Flavour Components Volatile flavour components were analysed using a method developed for solid samples (Przybylski, 1991). Briefly, 500 mg of milled buckwheat was placed into gas chromatograph (GC) injector insert and both ends were closed with purified glass wool. The inserts and glass wool were purified by heating at 380°C for at least 4 hours prior to use. The insert containing the sample was placed into the injector held at 110°C for 15 minutes and volatiles were transferred into the trapping column with helium used as carrier gas. The trapping column was immersed in liquid nitrogen during purging. The sample was removed from injector, pressure - 648-

equilibrated to working conditions, liquid nitrogen removed and run commenced. Volat~les were separated on fused silica capillary column, DB-5 (J&W, Folsom) at followmg parameters: column temperature programmed from 40·C to 210·C at, the rate of 2.5·~ per minute. Lower and upper temperatures were held for 4 and 15 mmutes , respectively. Separated compounds were identified by comparison of retention data to standard components. Quantification was performed using decane as internal standard. Oxidation products were expressed as percentage of total volatiles. RESULTS

Lipids Triglycerides, diglycerides, free fatty acids showed the most pronounced changes. In Fig 1 results of analyses are summarised. It is evident that triglycerides disappeared at the fastest rate while the amounts of diglycerides (DG) and free fatty acids (FFA) increased during storage at all conditions. Triglycerides degraded at the rate of 0.11 mg per week of storage while DG and FFA amounts increased at the rate of 0.05 and 0.16 mg per week of storage, respectively. At the end of storage period the amount of TG decreased by 3% however the amounts of DG and FFA increased by 23% and 27%, respectively. Storage of buckwheat under controlled atmosphere did not significantly decrease degradation of triglycerides, although formation of DG and FFA was observed at the lower rate. Like during storage under different humidity and temperatures again among free fatty acids unsaturated compounds were mainly present such as linolenic and linoleic acids, which are the best substrates for lypoxygenase oxidation. Flavour and Oxidation Products Changes in flavour and off-flavour components in Fig IB are summarized. Total amount of volatilelflavour compounds decreased with time of storage, whereas at slightly slower rate than during storage at elevated temperature and humidity. Fresh buckwheat contained about 16% of flavour components which were identified as oxidation products. Those components are typical products of oxidative degradation of unsaturated fatty acid but as in fried products they are forming characteristic flavour of the product. During storage in these condition increase in the amounts of oxidation products was observed. Observed changes in volatile flavour components were as follow: total volatiles decreased by 25% while the amount of oxidation products increased by 267%. From the same data rate of flavour components disappearance was 14.7 ng per week while oxidation products were formed at the rate of 13.2 ng per week. This rate indicates that oxidation process can playa significant role in off-flavour formation and is can be stimulated by enzymes, mainly hydrolases and lypoxygenases however chemical oxidation also can not be neglected. At the end of storage time over 43% of flavour components were oxidation products which at this concentration can affect off-flavour formation. Although storage under controlled atmosphere produced less oxidation products than formed during buckwheat storage under normal access of oxygen. Lower amount of oxygen available significantly reduced the amount of oxidation products. From analysed data it is evident that oxidation products formed from unsaturated fatty acids can play important role in flavour changes. Sensory evaluation of stored buckwheat samples confirm changes in flavour components

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REFERENCES Campbell, C. G. and Chubey, B.B. 1995. A delitiller for buckwheat samples. Can. J. Plant Sci. 65,771-773. Eskin, N. A. M., R. Przybylski, L. Malcolmson, D. Ryland and G. Mazza. 1998. The Effect of Temperature and Water Activity on Rutin, Chlorophylls and Colour of Stored Buckwheat. In: Current Advances in Buckwheat Research, Eds C. Campbell and R. Przybylski, Winnipeg, pp. III - 3-6. Marshall, H. G. and Pomeranz, Y. 1982. Buckwheat: description, breeding, production and utilization, In Cereals '78. Better Nutrition for the World's Millions. pp. 201-217, Am. Assoc. Cereal Chern. Marshall, H. G. and Pomeranz, Y. 1982. Buckwheat: description, breeding, production and utilization. In Y. Pomeranz (ed.): Cereals >78: Better Nutrition for the Worlds Millions.

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Amer. Assoc. Cereal Chern., St. Paul, MN, pp. 201-207. Mazza, G. 1986. Buckwheat browning and color assessment. Cereal Chern. 63(4), 361-364. Mazza, G. 1988. Lipid content and fatty acid composition of buckwheat seed. Cereal Chern. 65(2), 122-126. Mazza, G. 1993. Buckwheat. In Encyclopedia of Food Science, Food Technology and Nutrition, pp. 5] 6-52 1, Academic Press, London. Mazza, G. 1994. Storage processing and quality of buckwheat seed. In New Crops. (1. Janick and J. E. Simon, eds.) pp. 251-255, John Wiley & Soils, New York. Mazza, G., T. Cottrell, L. Malcolmson, B. Girard, D. Oomah and N. A. M. Eskin. 1999. Headspace gas chromatography and sensory analyses of buckwheat stored under controlled atmosphere. 1. Food Quality 22; 341-352. Przybylski R., Woodward, L., Eskin, N. A. M., Malcolmson, LT and Mazza, G. 1995. Effect of buckwheat storage and milling on flavor compounds. In Current Advances in Buckwheat Research, Vol. 2, (T. Matano and A. Ugitiara, eds.) pp. 783-787, Shinshu University Press, Japan. Przybylski, R. 1991. Effective trapping system for volatile components analysis in oils and fats. Proceedings of the Eighth International Rapeseed Congress, Ed. D.J. McGregor, Saskatoon, Canada, July 9-11, 3:861-866.

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