The Effects Of Different Processing Techniques On The Organoleptic Quality Of Soymilk Processing And Storage

Project and Seminar Material for Food Science and Technology (FST)

The Effects Of Different Processing Techniques On The Organoleptic Quality Of Soymilk Processing And Storage


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


His of Soymilk: 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.

Soybean composition (PREXIMATE), commercial soybean constitute and 2% hypocotyls and phumule. Proximate composition for whole beans and fractions are given in Table 1


Fraction Protein (Nx 6.25)Fat %Carbohydrate %Ash %
Whole bean4021344.9

The constituents of major interest oil and protein make-up about 60% of the bean, but about one third consist of carbohydrates including polysaccharides, stachyose (3.8%), raffinese 1.1% phosphatides, sterols, ash and other minor constituents are also depend on variety, soil fertility and weather conditions.

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:-

  1. Amino acids composition
  2. Presence of anti-nutritional factors
  3. Digestibility
  4. Overall composition of the diet
  5. 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.

Chapter Five

Discussion, Summary and Conclusion

5.1 Discussion

Soymilk is an idea medium for bacteria growth and hence and hence a thermal treatment is necessary to extend its shelf life. Heat processes are involved at several stages during soymilk preparation, including the pre-treatment of beans and extraction to produce the soymilk, followed by either pasteurization or sterilization to increase its shelf life. By controlling the microbiology of the product and packaging it in appropriate containers, the shelf life of soymilk can be greatly extended and the product can be distributed over a wider area.

Proximate analysis of the “soy milk” from each variety of soybeans shows that averagely it has a water content of 91.24, Protein of 2.74, fat content of 2.08, Ash content of 0.32 and Carbohydrate of 2.26 this agrees with the findings of Nelson et al. (1978) and Gesinde et al. (2008) with the exception of protein and carbohydrate content which is lower in their own report. This may be due to the variety of soybean used, the method of extraction and other equipments used (Gesinde et al., 2008). It has been reported that soybean varieties greatly affect the protein content and colour of soymilk (Min et al., 2005, Gesinde et al., 2008). Soy milk prepared from beans pre-soaked in NaHCO3 contained more protein and a higher viscosity than milk prepared from beans pre-soaked in Na2CO3. Soaking with NaHCO3 as well as blanching gave a higher protein content of soymilk because soaking gives a tender product which results in finer slurry and thus more filtrate will pass thru the filter cloth thereby increasing yield and subsequently the protein content of soymilk (Bourne, 1976). The low protein value for Na2CO3 method can also be because Na2CO3 reacts with protein and forms a complex, which reduces the protein availability of produced soymilk (Tunde-Akintunde and Souley, 2009).

The higher ash content of NaHCO3 could be due to more mineral being extracted in soymilk due to the action of the acid. These values are comparable to Onuorah et al. (2007) findings. The higher moisture content of Na2CO3 could be as a result of coagulation of protein and hereby restricting more water expulsions from the cake (Bourne, 1976). The carbohydrate content of NaHCO3 milk was higher and similar to that reported by Wikens et al. (1967). The fat content of NaHCO3 was higher and it correlated with the report obtained by Adetunji et al. (2006). Farinde et al. (2008) suggested that the total solid of soymilk could be improved by adding soybean flour to the soymilk.

Increasing the total solid increases the nutritive value of the product thereby improving the keeping quality.
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. Preservation of soymilk by refrigeration has been shown to be relatively effective in retarding microbial growth. The shelf life of pasteurized milk products subjected to ultra high temperature (UHT) is usually extended especially if adequately stored (Saidu, 2005). This can be done through the use of chemical preservatives to minimize food spoilage. In economically under developed countries, lack of functional storage facilities and the inadequacy of transportation and communications may increase the necessity of using certain food additives for purpose of preservation. In tropical regions, high temperature and humidity favour microbial attack and increase the rate of development of oxidative rancidity. Food additives might be used to supplement the effectiveness of traditional methods of food preservation rather than to replace these methods (Alais and Linden, 1999 cited in Egbo, 2012).

The sensory attributes of perceived color and flavor are the most important characteristics in soymilk because they are readily assessed by consumers. Soymilk when subjected to severe heating acquires a brown color and cooked flavor (Kwok et al., 2000 cited in Egbo, 2012). Kwok and Niranjan (1995 cited in Egbo, 2012) have demonstrated the effects of thermal processing on the quality of soymilk and concluded that the main chemical reaction that gives rise to heat-induced color and flavor changes is the maillard reaction. Most work done on soybean products made reference to future research to be done to improve colour, taste and aroma of soybean products either through flavour additives and heat treatments (Farinde et al., 2008; Ikpeme et al, 2009). It has been reported that the use of preservatives also reduced Staphylococcus aureus population in soymilk to less than hazardous level at the end of ambient storage and lag-phase periods were extended by the preservatives resulting in longer shelf life (Nwanebu, 1994 cited in Egbo, 2012).

The sensory evaluation shows that sample produced with Na2CO3 has a higher preference for smell and taste because the methods reduced the beany flavor as reported by Liu (1997 cited in Egbo, 2012). However these samples have the lowest preference in terms of colour. Tunde-Akintunde and Souley (2009) reported that from their results, they noticed that the sensory properties of soymilk increased with decrease in nutritional quality indicating that methods which increase sensory properties of soymilk by reducing its beany flavor have lower nutritional qualities. Wikens et al. (1967) found that the off-flavours of soymilk were present in the dry soybean but were formed during the processing and that blanching the beans in hot water prevented the formation of the strong beany flavours.

They attributed this result to the rapid heat inactivation of the lipoxidase in the soybean precluding its attacking the unsaturated fatty acid chains in the soybean oil to form a number of lower molecular weight compounds that have objectionable flavor impact. Lipoxygenase catalyze the hydroperoxidation of polyunsaturated lipids in the presence of molecular oxygen and the primary products are hydroperoxide. The volatile carbonyl compounds including aldehydes, ketones and alcohols are partly responsible for the objectionable odor and flavor in soymilk. During the preparation of soymilk, soybean is ground with water and the LOX activity is greatly enhanced when the soybean is damaged or crushed. Therefore the inactivation is carried out at a higher temperature of 80-100oC during the preparation of soymilk. Inversely at these temperature, protein molecules are denatured (Prabhakaran, 2005), therefore other methods (antioxidants) are sort to complement the use of high temperature.

Although soymilk is a potential substitute for cow milk and could be used for solving malnutrition problems in developing countries, its utilization is hampered by a number of factors. However, acceptability of soybean products has been enhanced by modification of processing methods. Some of the modified soymilk extraction methods include application of heat, soaking of soybean in ethanol or alkali and acid grinding (Iwe, 2003). Kolapo and Oladimeji (2008) reported on the use of natural flavourants to improve soymilk acceptability. It has been reported that pasteurization of vegetable milk extract at 121oC for 15 minutes effects maximum destruction of microorganisms and made the products microbiologically safe (Onweluzo and Nwakalor, 2009). The effect of pre-soaking soybean in solutions of various chemicals on the reduction of beany flavor in soymilk was investigated. Na2CO3 had a significant effect on the reduction of beany flavor in soymilk. Na2CO3 soaking at 1.25% for 12 hours was significantly better than NaHCO3 pre- soaking treatment. Beans pre-soaked in carbonate were easier to process than NaHCO3 (Khaleque et al, 1970).

The shelf life of the soy milk produced at room temperature was up to 4 days, this deviated from the average shelf life reported generally for most milk and milk- based products. This is the reason why several workers are exploring the use of chemical preservatives for prolonging the shelf life of milk products (Sumati and Shalini, 1986; Uriah and Iwagbe, 1990; Gesinde et al., 2008). Statistical analysis of the data on the organoleptic assay showed that there was no significant different among the variety for sweetness of their soymilk. There were no significant difference (P>0.05) in the color, odor and texture of the soy milks treated with NaHCO3 and Na2CO3. Benzoic and sorbic acid are among the most commonly used as preservatives in their salt forms (Sodium or potassium) (Wibbertmann et al., 2005). Potassium sorbate has been reported to be more effective against moulds involved in spoilage of foods at pH of 4.0 to 6.0 than against the bacterial flora especially lactic acid. Sodium benzoate has been reported to be less effective than potassium sorbate against moulds though the two preservatives are capable of inhibiting aerobic and catalase positive bacteria such as Staphylococcus aureus, coliforms and psychotropic spoilage bacteria (Nwanebu, 1994 cited in Egbo, 2012; Wibbertmann et al., 2005).

5.2 Summary

Soybean can be processed using various techniques into different products. Generally, processing treatment significantly affected the quality of the products. The milk products were highly acceptable. Fermentation increased the protein content of the product. Variations in chemical values of the samples were a function of processing treatment. The products were microbiologically stable during storage. the samples had no growth of microorganisms throughout storage. Based on these results, an acceptable standard procedure can be developed for processing soybean into various products with an effective process control programme.

5.3 Conclusion

The effect of certain preservatives at various concentrations within their maximum permissible levels along with pasteurization and refrigeration storage on the microbial keeping quality of soymilk used showed that soymilk samples blanched in NaHCO3, pasteurized at 75oC for 15 seconds and then formulated with 0.1%potassium sorbate and sodium benzoate in addition with either 200ppm propyl gallate or 100ppm propyl gallate and ascorbyl palmitate, gave soymilk of high microbial quality and shelf life stability. Study on the suspension stability of soymilk should be considered as the soymilk separated during the period of study unlike the most market soymilk which is relatively stable. Also other method of preserving soymilk, so as to extend its shelf life should be studied (carbonation).

In line with other studies, it was demonstrated that processing method, storage temperature and storage duration have significant combined effects on the proximate chemical composition and sensory attributes of soymilk. According to most authors, soymilk produced from flour produces better nutritional profile and more desirable sensory properties than milk produced from wet blanched beans. However, liquid soymilk produced from the traditional wet methods, are most stable in sensory attributes when stored at very low temperatures. Conclusively, the quest for cheap source of protein has enhanced small scale production of vegetable protein products of which soymilk is an example. Soymilk consumption has encouraged small scale production of the product under household condition with little or no regard to quality control measures. Soymilk therefore has the potential to substitute dairy milk.

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