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THE EFFECTS OF DIFFERENT PROCESSING TECHNIQUES ON THE ORGANOLEPTIC QUALITY OF SOY MILK PROCESSING AND STORAGE

ABSTRACT

This study examined the effects of different processing techniques on the organoleptic quality of soymilk processing and storage. The utilization of soybean for the production of soy milk was studied. Soy milk was extracted from whole and dehulled seed, pasteurized and fermented. All soy milk samples were analyzed for proximate composition (moisture%, ash %, total solids, fat) and the organoleptic tests (color, thickness, appearance, body, texture, taste, smell, flavor and overall acceptability) of the soy milk samples were evaluated to determine the shelf-stability of the products during refrigeration and room temperature storage. The moisture, protein, fibre, fat, ash, carbohydrate and total solids of soy milk from whole and dehulled seed differed significantly (p<0.05). There was marked variation in the % fat content of the products. The results of the sensory evaluation revealed that flavor with respect to taste and smell had significant influence (p<0.05) on overall acceptability of soy milk product. The sensory properties of yam bean yoghurt samples were compared with soybean yoghurt. The sensory properties showed that sample stored at refrigeration temperature maintained good quality up to 16 days storage while samples stored at room temperature were of poor quality by the 4th day. The implication of these results is discussed. So, the soy milk manufacturers need to improve on the sensory properties in particular flavor and taste for better consumer acceptability. Also, they may improve on packaging by labeling to specifications that precisely represent the content and type.

CHAPTER ONE

INTRODUCTION

Soybeans belongs to the family leguminous, subfamily  papiliondase and the genus Glycine Max. (Ricker and Morse, 1984), other nomenclatures which have been used include phaseolus Max, Soja Max Piper and Soja hispide moech. It is not known when this remarkable legume, soybean was first cultivated in China. However as the first  legume of which a written record was made. This was in the books of the Emperor  Shen hung, dated 1800BC which describes the five principal and sacred crops of China, rice, bean, wheat barely and millet. Giving expert advice on growing soybean which was cultivated more extensively in North than in Southern China, it reached Hapan and other countries in East Asia at an early date. Soybean contain about 46%  protein and 18% fat, characteristics which have influenced it’s history: the ancient Chinese evolved  methods of making from it’s preparations with high protein content for example, Curd and Shoyu, Shoyu is a dark brown liquid made by fermentation of a combination of soybeans and cereals (F.A.O. 1970). The Chinese also ate soybeans as a  vegetable after it has sprouted.

The soybean was first heard of in Europe in 1712 through the German Botanist Egelbant Kalmpfer who had visited Japan. In the 18th century, it was grown in some European botanical gardens (F.A.O, 1970), it is first appearance in the United States in 1804, when Commander Perry brought home two varieties from Japan (F.A.O, 1970). What was called the second stage in the history of soybeans did not begin until the first decade of the present century, when it become an important export from East – Asia at first mainly to Europe and alter to the importing countries was as a source of oil for soap making and other purposes and for the manufacture of livestock feed.

Then the third stage began in the early nineteen thirties, it is silent feature has been the large stage cultivation of the soybean in the United States, combined with the application of Modern Technology which enable it to be put to a variety of uses both as food and folder and as raw materials for manufacturing processes, while soybean has to a considerable extent becomes an industrial crop in the United States, it continues to be grown in East Asia as a food crop processed for consumption by time honoured  methods. (FAO, 1970). The fourth stage began during the first decade of the 20th century A.D. at the period in which this crop was first introduced of soybeans in Nigeria shows that middle belt of the country to be the best producer of soybean production (Ezedinmma, 1964). In Nigeria, nearly all of the soybean production estimated at 30,000 tons is used for human food. A response to increase in demand for soybean for soybean as a source of protein and vegetable oil, national programme in Nigeria have explained their research on the crop. Since 1987 (IITA; Annual Report 1985) currently more feather have been added to the number of products that can be obtained from soybeans in Nigeria, such products like soymilk as it had been recently demonstrated at the food investigation centuries in Enugu.

Soymilk in the traditional sense is simply an aqueous extract of whole soybean, A detailed description of the technique used for the preparation of the soymilk as well as its composition will be found in chapter 3. Soymilk according to the nutritionist a possible substitute for cow or human milk particularly in the feeding of infant who are allegic to animal milk or where cows milk may be found to be two expensive or unavailable.  Miller, (1962) soybean or vegetable milk or flu-changin chinse is reported to have been developed and used in china before the Christian era (paker and Morse 1943) by the philosopher who was credited with the first step in the processing of tofu and yuba. Then, the traditional milk is made by soaking the bean in water overnight, wet milling the bean, heating the wet mash to improve flavour and nutritional value and filtration. The milk produce is sold to the public in streets and canteens in china in 1984. In recent years large scale production ha evolved along with commercial marketing of soymilk in Hongkong, Taiwan, Thailand, South Korea, Sinapere, Malaysiaa and not the United States (Babara, 1984).

Uses of Soybeans

Soybeans are a native crop of Eastern Asia where they have `served as an important part of the diet for centuries. The Japanese for example obtain 12 – 13% of their dietary protein from soybean product, for many of their traditional soy foods, the oriental people soak soybeans in water and then grind or cook them. Hot water extraction of ground beans yields soybean milk  which is consumed as such or is treated with calcium salts to precipitate the protein plus oil in the form of bean curd or tofu, fermentation of cooked soybeans yield products including soy sauce, misso, notto and tempheh.

Except for soy sauce, one of the traditional oriental foods is consumed in significant amounts in this country. Soybeans are a relative new corner to the American scene. They have only been gown in quantity since the late 1920’s when soybean processing become an established industry, the two major products were oil and defaulted meals. In the mid – 1`930’s large  portion of the oil began to be used for foods such as shortening, margarine, cooking oil mayonnaise and salad dressing, because of its high protein content and good nutritional value, when properly processed, the meal was used primarily  for animal feeds.

Soybeans have expanded in the last 30 year from a minor crop to a major cash crops. Indeed in value to the farmer soybeans now rank second to corn and above wheat, potatoes, oats, cotton and a  variety of other crops better known to the consumers, only within the last ten years however, have every many edible products. Containing soybean derivatives been directly associated with their source. In shortening their presence was “hidden” by statements similar to the followings. ‘A blend of hydrogenated vegetable oils or in salad dressing, merely “vegetable oil or a blend of vegetable oil”. Today a long list of foods containing soybean derived product can be prepared by careful reading of the labels in the supermarket, yet most of these are even not specifically identified as soybean. Product from corn, wheat, oats and many other commodities are so labeled for example corn flakes, wheat, garn, oatmeal, but not soybean. There are several reasons for this an enmity, soybean have a short history of sue in the U.S.A. the flavour and texture of soybean products are comparatively strange to people outside the orient.

Although the Chinese and Japanese have covered soybeans into a variety of products most of these foods have little physical or flavour identity with the original bean. Some people agree that green soybean are a delicious dish when properly harvested and cooked but their sale and the sale and the ale of mature beans for baking are extremely small. Soybean products have problems related to their flavour and flavour stability to their ruction in foods and to their physiological effects. Despite these problems soybean oils have become a major material in our food industry. Soybean now supply more than half of the total visible fits and oils  consumed in the U.S.A.

NUTRITIONAL PROPERTIES OF SOYBEAN

Over 50 years ago Osborne and Mendel (1980) found that rates grew poorly when feed with raw soybean meal and that dry head did not improve the nutritional value of the meal. Rates grew normally, however when the meal was cooked on a steam for 3hrs. In the past 50yrs a vast literature was developed on the nutritive properties of soybean protein, but moist heat is still used to improve the nutritional quality of soybean protein product for foods and feeds. The literature on this subject is often confusing and contradictory ; two recent reviews gives concise summaries of pertinent work for the last 30yrs. Alleged anti-nutritional factors and protein quality therefore are discussed only briefly.

Anti-nutritional factors

Since moist heat readily inactivates the anti-growth factors raw soybean meal, many workers believe that the factors are protein-inhibitors and hemagluthins, non protein components such as sapynins have b suggested as anti-nutritional factors but recent work does not support this view.

TRYPSIN INHIBITORS

More than five trysin inhibitors are reported for soybeans but only two-the kenitz and the Bowman Birk inhibitors have been purified and studied in details Kaw soybean meal contains 1.4% kunity inhibitor and 0.6^ Bowman-Birk  inhibitor. Although both inhibitors are active against boline trypsin the kunity inhibitor has any how activity the esterase activity of human trypsin. The activity of human trypsin however is inhibited to a significant extent by unity inhibition when case is sued as a substrate to measure proteolytic activity. It is not known whether ingestion of the inhibiters affects the presence in humans.

From the practical standpoint, Trypsin inhibitors do not appear to be a serious problem in feeds and food since they are largely inactivated by moist heat. Condition of heating time, temperature, moisture content and particle size influence the rate and extent of trypsin inhibitors inactivation for example, atmospheric steaming (1000C) inactivates more than 95% of the trypsin inhibitor activity of raw, defatted soybean flakes in 15mins. Protein efficiency shows an accompanying increase in this same time and flakes of 19% moisture gave a higher protein efficiency ratio than flakes of 5% moisture. In contrast, steaming whole soybeans chips, or cotyledons for 20mins only partially inactivated trypsin inhibitors apparently because of the large particle size. Atmospheric steaming inactivates most of the trypsin inhibitor in whole soybeans in 15mins. In initial moisture content is 20%. If the beans are soaked in water overnight 60% moisture 25mins. In boiling water sufficient to inactivate the inhibitors. Small but measurable trypsin inhibitors activity  can often be deflected after heating the known stability of Bowman-kirk inhibitor suggested that the residual inhibitor may be of this types. Measurements of residual chymotrypsin inhibitor activity would clarify this point because the Bowman-kirk inhibitor is a strong inhibitor of chymotrtpsin.

At recent study reports trypsin inhibitor activity commercial protein isolate but no inhibitor was detected in canned frankfurters containing 1.5% isolate. The heat treatment during canning inactivated the residual inhibitor. Many of the conclusion drawn from studies on kunity inhibitor must be viewed with some reservations because of the heterogeneity of certain commercial preparation even when crystallized five times. The possibility that a protein impurities or a tightly bound non-protein impurity is responsible for some of the biological properties of the inhibitor has received slight  consideration until recently.

Hemagglatinins –Soybean contain at least four proteins capable of causing clumping of red blood cells of rabbits and rates in invitrotests. These proteins are designated haemagluttinins;  these proteins are in many legumes. Defected soy flour contains about 3%  lemaglutinins. The major hemagluttinin in soybeans has been insolated and characterized. It is a glycoprotein containing 4.5% mannose and 1% glucesanine and has a molecular weight of 110,00 and appear to contain two polypeptide chains. The ability of hemaggluttinins to cause clumping of red blood cells in a test tube serves as a useful assay procedure but there is no evidence that agglutination of red cells occurs when hemagluttinins are ingested. Hemagglutinins is readily inactivated by pepsin; thus it probably does not service passage through the stomach. Furthermore, undigested hemagglutinin would have to be absorbed from the intestine to come into contact with red blood cells an occurrence which seems unliky because of the high molecular weight of the hemagglutinin.

Soybean hemagglutinins are readily inactivated when maximum growth response is obtain. Hemagglutinins this ;present no known problems in foods of preparation includes proper heating of the soy ingredient at some step of processing. Soybean saponings – saponins are complex glycosides of triterpenoid alcohols and occur in soybeans to the extent of 0.5% and because of their polarity, the saponins are insoluble in hexane and remain in defatted meal; defatted meal contains 0.6^ saponins. Although antinutritional properties have been ascribed to soybean saponins, recent studies show t hem to be harmless when ingested by chicks rates and nice aft 0.5 to 3% of the diet. At the highest level the saponins content was about three fold higher than in a 50% soybean meal supplemented diet. Neither saponings nor sapogenine were found in blood  of rates, mice or chicks kept in diet containing  20% soybean seed, thus the saponins are not absorbed thy remain intact until they leave the enzymes in the colon. The saponin inhibit various enzymes including cholinesterase and chymotrypsin but inhibition is not specific. Soyprotein and other dietary protein will also bind saponins. Approximately 0.4% saponins were obtained from a laboratory preparation of soyprotein isolate when isolates where ehated in dilate and solutions crystalline bit apparently modified. Saponins were obtained. The effect of interaction of the saponins with soy protein is still unknown, the saponins are an extremely complex mixture and only limited separations have been obtained to date.

Protein quality of soybean.

Until the 1960’s information on the nutritive value of soybean protein was largely limited to defatted flakes, meals and flours. Moreover most of the studied were concerned with use of soybean means as an animals feed. Since commercial introduction of concentrates and isolates in 1959 and their increasing use in foods, these fractions have received considerably more attention studies with human, however, are still limited. The quality of soy protein depends on several factors:-

a)    Amino acids composition

b)   Presence of anti-nutritional factors

c)   Digestibility

d)  Overall composition of the diet

e)   Nutrient requirement of the species involves. Item a, b, and c are of primary importance in considering the various soy protein forms as protein sources. In the preparation of isolates for example fractionation occurs; this results in a change in amino acid  composition as well as in removal of the antinutritional factors occurring in the whey, items of and e are of greater importance when a specific food is being considered i.e. an infant food dietary item or a soack food nutritional requirements for an infant differ greatly from the needs of an adult who may be trying too loose weight.

Aims and objectives of the project   

The processing of soybeans into soymilk is aimed at gaining consumer acceptance of the legume by removal of the toxicants that contain and also improving organoleptic qualities of soymilk with special consideration to some adverse effect of these operation in soymilk  quality.

This project re views the effects of different methods used in the processing of soybeans into soymilk on the quality of the milk produced during processing and storage.

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