Chemical properties analysis of soygurt with ginger (Zingiber officinale var.roscoe) extract as functional foods

The processing of soy milk into soygurt was an effort to eliminated the soybean flavor. Several studies showed that plain soygurt still had soybean flavor. The addition of (Zingiber officinale var. Roscoe) extract was an alternative to eliminate the distinctive soybean flavor. This experiment aimed to study the chemical properties of soygurt, which consist of protein, fat, ash, lactic acid, pH. This research used a completely randomized design with one factor of ginger extract concentration (i.e. 4%, 5% and 6%) and all treatments were carried out in duplicate. The collected data were analyzed by One Way ANOVA. If the result was significant (< 0.05), it would be processed by the DMRT test. The results showed the levels of chemical properties of soygurt were 4.507-4.987% of protein; 2.859%-3.220% of fat 0.455-0.56% of ash, 1.710-2.068% of lactic acid and 3.965-4.230 pH value. The experimental results showed that the addition of ginger extract was also proven to significantly affect the chemical properties of soygurt. The addition of ginger (Zingiber officinale var. Roscoe) extract could increase the levels of protein, ash, lactic acid and could reduce fat levels and pH value.


Introduction
Functional foods were beneficial to the body in addition to the function of basic nutrients which consisted of several bioactive components, such as isoflavones, dietary fiber, prebiotics (oligosaccharides), probiotics (lactid acid bacteria) [1]. Yogurt was one of the probiotic foods developed in the market. Yogurt made from cow's milk and, currently, various innovations were carried out to increased the diversity of this functional food, for example, soygurt. Soygurt was made from soy milk fermented by the lactic acid bacteria of S. Thermophilus and L. Bulgaricus [2]. Soy milk could be a substitute for cow's milk, especially for those who suffer lactose intolerance [3]. Soy milk contained 3.50 gr protein and 2.50gr fat [4]. However, soy milk produced a distinctive soybean flavor caused by the lipoxygenase enzyme derived from soybeans. Soy flavor could be reduced by soaking, boiling, fermentation and adding flavor. The process of soygurt became an alternative to eliminated the soybean flavor. Soygurt could become a functional food caused by the combination of probiotics and prebiotics that was made from soybeans (oligosaccharides) and probiotics from lactic acid bacteria L. acidophilus [5] [6]. Nevertheless, plain soygurt had a distinctive soybean flavor [7]. Therefore, additional ingredients were needed to improve the flavor of soygurt. Natural ingredients added could derive from Indonesian herbs, such as ginger which able to reduced soybean flavor. [8].
However, there was no further research on the chemical properties of soygurt with the addition of elephant ginger extract. Ginger contained a protease enzyme called Zingibain [9] which could help the coagulation protein processed in yogurt [10]. Ginger also had the ability to maintain food quality as an antimicrobial against pathogenic microbes which could inhibit the bacteria C. Albicans [11]. This research aimed to analyze the effects of addition elephant ginger extract soygurt towards the chemical properties consist of protein, fat, ash, lactic acid levels, and pH values.

Preparation of soygurt elephant ginger
The soy milk used soybeans of anjasmoro variety and the ginger extract used Zingiber officinale var. Roscoe types were bought from Balitkabi and the local market in Malang, East Java, Indonesia. The first process of made soygurt mixed 100 ml of soy milk with 15 grams of skimmed milk powder, 10 grams of sugar, and the addition of elephant ginger extract i.e of 4%, 5%, and 6% (v/v). Then, the pasteurization step was carried out for 30 seconds at 75 o C. Next, the temperature dropped up to 43 o C and an inoculation process was carried out with the addition of lactic acid bacteria (L.bulgaricus, L.acidophilus, and S.thermophilus) 5% (v/v). The last step was the fermentation process in an incubator at 43 o C for 4 hours and let it sit at 25 o C for 12 hours.

Methods and analysis
This experimental research used a completely randomized design. The treatment was the addition of elephant ginger extract to soygurt, A1 (concentration of elephant ginger extract 4%), A2 (concentration of elephant ginger extract 5%), A3 (concentration of elephant ginger extract 6%) and all treatments were carried out in duplicate. Then, each treatment was analyzed for the protein levels (semi-Kjeldahl micro method), fat levels (soxhlet extraction method), ash levels (dry ashing method), lactic acid levels (titration method) and pH value (used a pH meter). [12] The data were analyzed of chemical properties by One Way ANOVA to rate the differences in the product. If the ANOVA test results had a significant difference with the significance level (<0.05), a further test would carried out by DMRT (Duncan's Multiple Range Test) to determine the differences in each treatment.

Results and Discussion
The results of the addition of elephant ginger extract with a concentration of 4%, 5% and 6% into soygurt showed significant differences in chemical properties included the levels of protein, fat, ash, lactic acid, and pH value.

Protein levels
The addition of elephant ginger extract to soygurt could increase the protein levels as shown in Table  1. This was caused by the raw materials contained in soygurt. Ginger contained 1.5 grams/100 grams of protein [4], the more elephant ginger extract added to the mixture, the levels of soygurt protein also increased. It was caused by activated of the protease enzyme contained in ginger. Zingibain had protease enzyme that could assist the process of coagulation milk into cheese [9], [13]. Based on the aforementioned theory, zingibain helped speed up the process of protein coagulation in soygurt. The protein hydrolysis process could increase protein levels in a food product [14]. In the process, zingibain as a protease enzyme in ginger could increase protein levels which causes protein hydrolyzed into large amounts of peptides. The increased protein levels in this research were appropriate with other research [15] that the addition of ginger paste on the chicken could maximize proteolytic performance so that the protein levels increased up to 23.77%. The other research also proved the increasing protein levels in soy milk powder with the additional ginger extract [16]. Protein levels had fulfilled the yogurt standard minimal 2.7% [12] and higher than plain soygurt protein levels in the USDA which was 3.53gr [17]. Table 1 indicated a noticeable difference that the higher the concentration of elephant ginger extract could reduce soygurt fat levels. The decline was caused of the lipase enzyme in the ginger [18]. Lipase enzyme was an enzyme that breaks down fat into fatty acids. It would transformed into fatty acids either saturated or unsaturated [19]. The processed soygurt with the addition of elephant ginger extract contained a lipase enzyme, especially in the fermentation process that used L.acidophilus lactic acid bacteria also helped the activity of the lipase enzyme more optimally to reduce fat levels. The higher the concentration of addition elephant ginger extract, increasing the performance of the lipase enzyme that could reduce the fat levels in soygurt. The reduction in fat levels following a research [19] that the higher the concentration added the fat content of yogurt decreased to 4.08%. The fat levels contained in soygurt products had met the standardization in Indonesia [11] soygurt with the addition of ginger extract of 4% and 5% included in the standard yogurt of at least 3%, while soygurt with the addition of elephant ginger extract 6% included in the category of low-fat yogurt ranges from 0.6-2.9%. It also added to the functional value of helped the normal maintenance for cholesterol patients it caused ginger contained gingerol that could assist in reduced cholesterol levels [18].

Ash levels
Ash levels were factors to determine the quality of food products commonly referred to as organic substances or minerals. The addition of elephant ginger extract increased the ash levels of soygurt as shown in Table 1. The amount of ash levels contained in a food product depends on the magnitude of the material of mineral content used [16]. The mineral could obtain from various foodstuffs. Based on a study [20] soybean milk of anjasmoro varieties had ash levels of 5.88%. Elephant ginger also had a high ash content that is 6.60-7.70% [20]. The ash levels contained in soygurt had qualified the quality of yogurt [12] with a maximum ash level of 1.0%. It could categorize as a functional food product development. It caused the addition of elephant ginger extract to soygurt which could increase the nutritional value of ash or mineral. Soybean contained iron, phosphate, copper, manganese and calcium, and zinc. The fermentation processed soybean could increase the availability of iron and hydrolyzed acid phytate on soy [21].

Lactid acid levels
The result in Table 1 indicated that the addition of elephant ginger extract on soygurt could increase lactic acid levels. The acidity of yogurt is inversely proportional to pH levels. The lower levels of pH caused the increasing levels of lactic acid in soygurt added with elephant ginger extract. The higher the addition of the concentration of elephant ginger extract in soygurt increased the lactic acid bacteria which could increase the acidity in yogurt [22]. Lactic acid levels in soygurt with the addition elephant ginger extract had fulfilled the Indonesian standard yogurt [12] concentration of 4% and 5%. While the addition of elephant ginger extract with a concentration of 6% in soygurt had a high acidity level exceeds the Indonesian standard yogurt with range 0.6-2% [12]. Therefore, soygurt with a concentration of additional elephant extract of 4% and 5% could be functional food products. L.acidophilus in soygurt could utilize lactose and a sucrose supplement contained in milk so that the metabolic activity optimally and produced high lactic acid [23].

pH value
The additional elephant ginger extract could reduce the pH value in soygurt as shown in Table 1. It was caused by the raw material used. Based on a study the combination of starter on soygurt showed the combination of L.acidophilus, L.bulgaricus, and S.thermophillus bacteria could reduce pH levels up to 4.38 due to the change in sugar into organic acids [23]. Organic acids that were formed dissociated in the form of ions H + [24]. The decreased pH levels caused by the increased activity of lactic acid bacteria in the fermentation process and the occurrence of lactic acid was production derived from carbohydrates in soy milk [25]. The fermentation process was optimal because there were other carbohydrate sources derived from sucrose, skim milk (lactose), the starch in elephant ginger [7]. The higher concentration of added elephant ginger extract could increase the lactic acid bacteria in yogurt [22]. The more lactic acid bacteria used, the metabolites especially lactic acid that could dissociate into ions H + thus decreased pH value [24]. Soygurt with the addition of elephant ginger extract proved to decrease pH value and increased lactic acid levels. It was in accordance with the result of research by Putri et al., (2018) that the higher concentration of addition of ginger could reduce the pH value [26]. It fulfilled the Australian fermentation food standard with pH maximum 4.5 [27]. Therefore, soygurt products could be one of the potential products as functional foods.

Flavor soygurt
Soygurt flavor changed with the addition of elephant ginger extract caused by changes in lactic acid levels and pH values. Table 1 showed that lactic acid levels increased, affecting the flavor of soygurt. In addition, the flavor in soygurt with the addition of elephant ginger extract was influenced by the decrease in pH value in Table 1 which showed a high acidity level so as to increase the sour flavor in soygurt. The sour flavor of soygurt with the addition of elephant ginger extract with a concentration of 4% to 6% could eliminate the soybean flavor from soy milk and improve the quality of soygurt.

Conclusions
The addition of elephant ginger showed significant differences (<0.05) in soygurt chemical properties. The protein levels obtained ranged 4.506%-4.987%, fat 2.8595-3.220%, ash 0.455-0.560%, lactic acid 1.710-2.068%, pH value 3.965-4.230. Based on the results of the chemical properties the higher amount of ginger extract added could increase the value of protein levels, ash levels, and lactic acid levels, but could reduce the levels of fat and pH levels. The added concentration of elephant ginger extract was not more than 5% to be recommended as a functional food product because the value range of chemical properties had fulfilled the quality standard of yogurt.