Comparative Study on the Proximate and Sensory Properties of Soymilk Steeped With Ascorbic Acid
This study examined the use of ascorbic acid as preservative on the shelf – life of soymilk stored at different temperatures. The utilization of soybean for the production of soymilk was studied. Soymilk was extracted from whole soybeans, and pasteurized. All soymilk sample were analyzed for proximate composition (fat %, ash%, total solids, protein%, titrable acidity and moisture%) and the organoleptic test (appearance, colour, aroma. Taste, consistency and overall – acceptability) of the soymilk samples were evaluated to determine the shelf-stability of the products during refrigeration and room temperature storage. The fat, ash, total solids, protein, titrable acidity and moisture of soymilk from whole soybeans seeds differed significantly (p < 0.05). The results of the sensory evaluation revealed that aroma with respect to appearance and consistency had significant influence (p < 0.05) on overall acceptability of soymilk product. The sensory properties of soymilk steeped with ascorbic acid samples were compared to soymilk without ascorbic acid. The sensory properties showed that sample steeped with ascorbic acid and stored at refrigeration temperature maintained good quality up to 12 days storage, while samples stored at room temperatures were of poor quality by the 4th day. The implication of these results was discussed. So, the soymilk manufacturers need to improve on the sensory properties in particular taste, aroma for better consumer’s acceptability, also, they may improve on packaging by labeling to specifications that precisely represent the content and type.
1.1 BACKGROUND OF THE STUDY
Soymilk is an aqueous, white, creamy extract produced from soybeans which resembles cow milk, both in appearance and consistency. (Richard and Martins, 2008). It is a highly nutritious food drink which contains protein, fats, carbohydrates, vitamins and minerals. It is because of this nutritious value and comparative low cost that soymilk plays an important role in the dietary need of people in most developing countries. (Wilson, 1995).
Soymilk is a traditional oriental food beverage that is grown in popularity in the United States and the world (Jimoh and Kolapo, 2007). Soymilk which is a watery extract of the whole soybean is rich in water soluble protein, carbohydrate and oil (Adebayo – Tayo et al, 2008). Soymilk is made by soaking soybeans in water before grinding and straining (Iwe, 2003, Kolapo and Oladimeji, 2008).
Soymilk is produced in different ways. The most common method is the Illinois method, which involves grinding of the soybean in hot water to obtain the milk (Iwe, 2003). Other methods include wet extraction and dry extraction (Hackler et al, 1962). It has been reported that the shelf life of soymilk is very short (Nwanebu, 1994 cited in Egbo, 2012).
This is as a result of the PH of the activities of the various micro-organisms contained in the milk, which may have been inherently present in the soybean as reported by Adeboya – Tayo et al (2009).
Nwanebu (1994 cited in Egbo, 2012), or due to inadequate processing and post – processing, contamination (Adeleke et al, 2009).
Changes associated with these activities vary, but usually include increase in PH, increase in titratable acidity, curdling and separation of curd and whey (Nwanebu, 1994 cited in Egbo, 2012, Adeleke et al, 2000; Adebayo – Tayo et al, 2009; farinde et al, 2008). Although there are some soymilk in the Nigerian market the ones that are shelf stable are scarce. This is because in Nigeria and most West African countries, soymilk is produced mostly at home under not very hygienic conditions and is thus prone to contaminations and spoilage by the micro – flora of the raw materials and utensils. The metabolic products of these organisms as well as their presence in soymilk, pose health hazard to the consumers.
Soymilk can be produced by different methods. The traditional method or cold grind method involves soaking the beans for 12 to 24 hours at room temperature. Water is frequently changed. Soaked beans are ground to fine paste using a food chopper or in stone mill. Water is added to the mass during grinding (ratio is 1:3 of beans to water). The resulting slurry is boiled to foaming for one hour with continuous stirring and later strained through Cheescloth (Iwe, 2003).
Recently, the consumption of soymilk has greatly increased for reasons which include poverty alleviation and because it is recommended for people that cannot tolerate lactose since it does not contain lactose. (Iwe, 2003) it is continuously being used as a substitute to cow milk in most remote areas of Nigeria and indeed Africa. This may also be because it has few other known advantages over cow milk e.g. it has a beneficial effect in the prevention of protein energy malnutrition in infants and growing young children as well as in the prevention of osteoporosis and kidney disease (Messina, 1995).
The nutritious nature of soymilk however, makes it prone to microbial attack if not properly processed and stored as the nutrients it contains are also required for the growth of most spoilage orgainsims. A large number of micro – organisms such as mesophilic aerobic bacteria, coliforms, yeasts and mould are known to be responsible for the spoilage of soymilk, producing undesirable changes in the milk (Osuntongun and Aboaba, 2004).
Soybean (Glycine max) is legume of an exceptionally high protein content ranging between 38% and 42% with lysine constituting a substantial proportion (Nwanebu, 1994 cited in Egbo, 2012; Lawson, 2004). Soybean is a rich oil seed crop with about 18% fat and 40 -48% crude protein. It is particularly noted for its richness in lysine, arginine, crysteine, leucine and methionine (Rastogi and Singh, 1989; Riaz, 1999; Sharma, et al 1999). It also contains minerials and some vitamins like calcium, iron, vitamin A, riboflavin and other trace elements (Cronan and Atwood, 1972). It can be conveniently consumed as powder milk or tofu (lu, etal 1980). However, some anti-nutritional factors like proteinase inhibitors, alkalacids and tannins may sometime weigh down the benefits of its whole unprocessed consumption, as these substances are not well digested by monogastric like man.
Ascorbic acid (C6H8O6) is a naturally occurring organic compound with antioxidant properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. (Lachapelle, M. Y., Drowin, G. 2010). Ascorbic acid is vitamin found particularly in citrus fruits and green vegetables. It is essential in maintaining healthy connective tissue and it also act as an antioxidant. The chemical properties of ascorbic acid provide a wide range of industrial applications. The use of ascorbic acid or vitamin c depends on its chemical properties as an antioxidant or on its health – related properties. Is mainly applied as an additive to food and feed to enhance product quality and stability.
This means that ascorbic acids added to foodstuffs during processing or before packaging protects color, aroma and nutrient content. Ascorbic acid (vitamin c) is a powerful antioxidant and offers a wide range of support for the human body. It provides support from numerous physiological functions, including vascular integrity and immune function. Vitamin c acts as an antioxidant, which means it keep foods from rating with oxygen when they are exposed to air.
1.2 STATEMENT OF THE PROBLEM
Milk product from soybean is characterized by beany flavor. Therefore, there is need to produce soymilk product without a beany flavor, by a natural process of removing or reducing the beany compounds through steeping with ascorbic acid.
Using soybean to produce milk instead of raising Cows may be ecologically advantageous, because the amount of soybean that could be grown using the same amount of land would feed more people than if used to raise Cows. Cow milk is beyond the reach of average consumers due to relative high cost. Soybean is a cheaper source than cow milk and it is highly nutritious and compares favourably with animal protein, it also serves as an alternative for individuals that do not tolerate lactose. Also soybeans plant is a legume; it also replenishes the Nitrogen content of the soil which it is grown.
1.4 OBJECTIVE OF THE STUDY
The objectives of this study are:
1. To produce soymilk steeped with ascorbic acid and well determined the best accepted sample sensory.
2. To determine the proximate, sensory and keeping quality of soymilk steeped with ascorbic acid.
3. To assess the effect of keeping methods of soymilk, and also the effect of the quality guided sensory.