الفهرس 
Introduction and Review of LiteratureOnly 14 pages are availabe for public view
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Abstract
Soymilk is a water extract of soybean that may afford advantages in terms of nutrition and health, since it contains no cholesterol or lactose and only small quantities of saturated fats Economically it may provide a solution of milk shortages and reduces the price of dairy products.
Lactic acid bacteria, Streptococcus salivarius subsp. thermophilus and Loctobacillus delbrueckii subsp bulgaricus and Bifidobacterium ssp are considered to be probiotic. Bifidobacterium species are a major component of the intestinal flora and can exert beneficial effects including the reduction of serum cholesterol, activation of the immune system and inhibition of the growth of potential pathogens that may cause infectious diseases.
The objectives of this study were to examine the activity of Bifidobacteria in soymilk along with standard yoghurt culture. Four species of Bifidobacterium were used, namely :
Bifidobacterium adolescentis.
Bifidobacterium angulatum .
Bifidobacterium longum.
Bifidobacterium bifidium.
Standard yoghurt culture consisted of :
Loctobacillus delbrueckii subsp bulgaricus .
Streptococcus salivarius subsp. thermophilus.
As, recently there have been growing interest in the manufacture of functional foods involving the use of soybeans and productions of dairy like products. The use of the mentioned bacterial species in the production of probiotic soy yoghurt were also assessed.
The obtained results were discussed under the following topics:.
1. Growth and activity of some Bifidobacterium spp:.
Growth: All Bifidobacterium spp.showed a similar growth profile and including bile salt (0.3%) in the MRS medium apparently had no effect on the growth profile of all species, although the growth was reduced. B angulatum and B.longum were more resistant to bile salts than B bifidium and B adolescentis .
Adhesion to intestinal epithelial cell: The results showed that B.longum had better adhesion followed by B angulatum and B bifidium with B adolescentis being the least.
Activity in soymilk: This was assessed by following the changes in titratable acidity and pH during incubation at 37ºC for 48h. In general, the pH of soymilk decreased and TA increase as fermentation time increase. B. adolescentis was the most active species followed by B. bifidium, then B. agulatum and B.longum being the least active species.
. Mixing two species of Bifidobacterium together, acid production was in the followeing descending order (B.adolescentis +B.bifidium,), (B.longum+B.bifidum), (B.adolescentis+ B. angulatum) , (B. adolescentis + B.longum)and (B. angulatum +B.longum). Ingeneral , acid production was comparatively less with mixed species compared with individual spp
. Mixed cultures of Bifidobacterium and lactic acid bacteria produced more acidity and lower pH values than that produced by pure bifidobacteria single or mixed. A mixed culture of bifidobacteria and lactic acid bacteria is suggested to be used to ferment soymilk.
2. Preparation and properties of probiotic soy-yoghurt:
Composition of soymilk : The resultant water extract contained 1.5% fat 4.2% protein and 9.1 % total solids, acidity was 0.31% and pH was 6.67 compared with buffalo’s milk which contained 6% fat , 3.6% total protein 15.3% total solids , 0.15% and pH value 6.65.
Preparation of soy yoghurt : Four starter cultures were used :
1) Standard yoghurt culture (SYC)+ B longum .
2) Standard yoghurt culture (SYC)+ B angulatum.
3) Standard yoghurt culture (SYC)+ B bifidium
4) Standard yoghurt culture (SYC)+ B adolescentis.
Yoghurt preparations were made from.
1) Pure soymilk.
2) Pure baffalo’s milk.
3) 1:4 Soymilk / buffalo’s milk mixture.
4) 1:1 Soymilk / buffalo’s milk mixture.
Properties:
A: Acid production:
. The rate of acid production was apparently faster with SYC+ B adolescentis starter culture than the other three types of starter.
. Acid production was more in buffalo’s milk and the mixtures with soymilk than pure soymilk.
. Including 0.1 % vanilla in yoghurt milk had no effect on the rate of acid production.
. No major changes in acidity or pH in both unflavoured or flavoured (0.1% vanilla) as a results of refrigerated storage for 12 days.
B: Production of flavour components:
Lactic acid: fresh yoghurt preparations had a pH values ranged from 4.58 to 4.00 and acidity values ranged from 0.55% to 0.88% which were more or less closser to lactic acid values reported in the literature ranged from 0.502 to 0.848 /100g.
Volatile organic compounds: The volatile organic compounds were expressed as μg acetic acid /100g. It mainly represents the organic acids ,
formic, acetic, propionic and butyric . The results showed that the production of these compounds depended to a large extent on the type of starter culture used and the type of yoghurt milk. Also, the stability of these compounds during refrigerated storage depend on both type of yoghurt milk and the type of starter. The presence of vanilla had no effect on the concentrations of volatile organic compound produced and did not affect its stability profile during storage.
Diacetyl:
. The results demonstrated that the amount of diacetyl produced was more with SYC+BA starter culture, followed by SYC+BL, SYC+BN and SYC+Bb.
. It was produced in higher quantities in dairy yoghurt and 1:4 soymilk /buffalo’s milk yoghurt than both pure soy yoghurt and 1:1 soymilk /buffalo’s milk yoghurt
. The presence of vanilla had either slight or no effect an the amount of diacetyl produced.
. The stability of diacetyl during refrigerated storage varied from one yoghurt preparation to another and from one type of starter to another.
Acetoin:
. SYC+BA starter cultured produced very high concentrations of acetoin in all yoghurt preparations compared with the other three types of starter culture.
. The values were much higher in dairy yoghurt and 1:4 mixture soymilk /buffalo’s milk yoghurt .
. Stability during refrigerated storage varied depending on yoghurt milk and type of starter used
. The presence of vanilla had no effect on the concentration of acetoin produced ,but affected the stability profile during refrigerated storage
Firmness of yoghurt gel.
. Soy yoghurt had a firmer gel than dairy yoghurt and firmness in yoghurt mixture depend on the ratio of soymilk in the mixture.
. All yoghurt preparation showed a noticeable increase in gel firmness with refrigerated storage.
. The presence of vanilla caused a pronounced reduction in gel firmness in all yoghurt reparations.
3: The survival of lactic acid bacteria and Bifidobacteria and sensory assessment of yoghurt preparation :
Survival of starter culture
. The results showed some variations between yoghurt preparations in the number of lactic acid bacteria and bifidobacteria, depending on the type of starter used.
. Both lactic acid bacteria and bifidobacteria showed a maximum number on the 3rd day of refrigerated storage.
. The numbers of counted bacteria start to decline on the 8th and 12th day of storage
. The over all numbers of bacteria count either of that SYC bacteria or bifidobacteria were within the recommended numbers even after 12 days of storage.
Sensory evaluation:
. The over all scores indicated that soy yoghurt and that made from 1:1 soymilk /buffalo’s milk were quite unacceptable, because of the quite clear beany flavour and chalkiness.
. Dairy yoghurt and 1:4 soymilk/ buffalo’s milk yoghurt made with SYC+BL and SYC +BN were highly acceptable.
. The presence of vanilla slightly increased flavour acceptability.
It was suggested that mixing soymilk with buffalo’s milk at 1:4 ratio would be the maximum for the production of acceptable functional yoghurt.