الفهرس 
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Abstract
Recently, Low-calorie, and low-nutrient foods have gained favour among consumers. Because of its great nutritional content and beneficial effects on health, yoghurt, a fermented dairy product, has acquired particular attention and commercial significance. In recent years, the market for functional and diet foods—including fermented dairy products—has expanded quickly.Consumption of whole dairy products (e.g., full fat yoghurt) has decreased due to increased awareness of the potentially harmful effects of fats on consumers’ health; as a result, consumer dietary patterns have changed, and market interest has shifted in favour of low or non-fat dairy products (Brennan & Tudorica, 2006). Unfortunately, manufacturers face low consumer acceptance and preference due to the lack of functional properties of left-out fat, which results in inferior organoleptic quality of products.
The texture and syneresis of non- or low-fat yoghurts are not the same as those of full-fat yoghurts (Caric et al, 2011). Therefore, the addition of soybean hydrolysate allows low or/non-fat yoghurts to be obtained that maintains good sensory properties.
In general, the work of the present study revealed the following: -
-The formation of bitter peptides arising as a natural degradation of soybean isolate by trypsin.
- During hydrolysis with pepsin enzyme for 180 min no bitterness was observed
- Results showed that the best ratio of SPH could be added 5% and 10% was added as the fat substitute for non-fat yoghurt.
- Addition of soybean hydrolysate with or without probiotic bacteria had strong effect on pH changes during fermentation time.
- During storage the rate of pH decrease was higher with treated samples.
-The soybean hydrolysate strongly decreased the fermentation time of yoghurts.
-The non-fat yoghurt samples showed the lowest (WHC). While the addition of 10% soybean hydrolysate improved the WHC of yoghurt.
-The highest value for firmness was found for full-fat yoghurt (C). While soybean hydrolysate increased the firmness of the yoghurt during storage.
-The soybean hydrolysate had a significant (p≤0.05) effect on syneresis at 1 day and during storge at 4°C.
-The treated samples with soybean hydrolysate and probiotic bacteria produced higher quantities of acetaldehyde, diacetyl, and acetoin
-The yoghurt samples supplemented with 10% soybean hydrolysate had the highest values of the total phenolic content (TPC) and total flavonoid (TFC). Mean while the control samples with or without probiotic bacteria had the lowest values of (TPC)and (TFC).
-The soybean hydrolysate increased the antioxidant capacity in non-fat yoghurt at 1st day.
- The lows values of antioxidant activity was recorded in full fat- yoghurt.
- The radical scavenging activity increased for all samples up to 5th day. Then little decreased was observed of 7 days.
- The highest values of total free amino acids had been recorded in samples supplemented with 10% soybean hydrolysate and probiotic bacteria.
- On the other hand, the soybean hydrolysate improved the viability LAB and probiotic counts at initial stage and enhanced the growth of probiotic bacteria during storage period.
- It can be concluded that using 5% soybean hydrolysate with probiotic bacteria in associate with common yoghurt culture had been most preferable in non-fat yoghurt in all features of the sensory properties at zero time and during storage.
According to Hashim et al, (2021) the World Health Organization (WHO) reported an increase in the number of people suffering from civilizational diseases such as obesity, diabetes mellitus, and cardiovascular disease. As a result, the global production of non-fat or low-fat dairy products has increased significantly.