1. Introduction
Soybean (
Glycine max L.) sprouts have been established as one of the major vegetables in Korea for a long time. Therefore, large amounts of soybean sprouts are produced in Korea each year [
1]. Various unwanted constituents or their functions in soybean seeds, for instance, trypsin, chymotrypsin, lipoxygenase activity, phytic acid, and oligosaccharides can be removed or reduced during germination [
2,
3,
4]. On the other hand, the amounts of other desirable constituents such as vitamins, phytosterols, tocopherols, and isoflavones could be increased during the period [
3,
5]. In addition to nutritional value, germination also improves textural and organoleptic characteristics of legume seeds [
6,
7,
8,
9].
Isoflavones are a vital group of phytochemicals in soybean sprouts. Consumption of soy products containing isoflavones reduces depressive symptoms during pregnancy [
10]. High dietary isoflavone intake may significantly increase fertility in humans [
11]. Intake of soy foods, high in isoflavone/polyphenolic molecules, from conception was found to be advantageous in reducing prostate weight and white adipose tissue deposition while increasing testicular weight, Sertoli cell area, and seminiferous tubule volume in rats [
12]. In another report, isoflavones from soy foods were found to be associated with reduced risk of ovarian cancer in southern Chinese women [
13].
Soybean sprouts can be produced without using advanced technologies and also can be grown in a considerably short time which are added advantages in their production. Soybean sprouts are an inexpensive food sources to supply dietary functional materials [
14]. Soybean sprouts can also be used in producing cosmetic products with anti-aging and skin whitening effects [
15].
Various experiments have been conducted to enhance the nutritional and functional properties of soybean sprouts since germination is one of the economical and effective methods to increase its food value [
16]. Calcium chloride was used to treat seeds and sprouts to enhance the yield and quality characteristics of soybean sprouts [
17]. Soybean seeds were exposed to ultrasound treatment and this improved the edibility and nutritional quality of sprouts [
18]. Macronutrients, phytochemicals, and antioxidant activities of soybean sprouts were manipulated with or without light exposure [
19]. Similarly, soybean seeds and sprouts were exposed to gamma radiation to increase the microbial safety [
20]; zinc sulphate solution was sprayed to enrich the zinc content in soybean sprouts [
21]; various light treatments were imposed to influence the isoflavone content in soybean sprouts [
22]; bacterial strains were inoculated to investigate their effect on bioactive compounds and antioxidant potentials of soybean sprouts [
23]; grapefruit seed extract, chitosan, and phosphate buffer treatments increased the yield and inhibited sprout rot [
24]; quality of soybean sprouts was increased with
ginseng treatment [
25]. In addition, various synthetic plant growth regulators such as Indolbi (INB) and 6-benzylaminopurine are also used to enhance yield and nutritional values of soybean sprouts [
26]. However, due to potential health hazards, the use of such synthetic chemicals in food products is generally less preferred by consumers.
Very limited studies have been conducted to investigate the effect of persimmon fruit on soybean sprouts although persimmon is rich in different nutrients and phytochemicals [
27,
28,
29,
30]. Persimmon also contains a flavonoid fisetin, an anticancer agent [
31]. Our recent report [
32] shows that seed treatment with persimmon fruit powder enhances the yield and food values of soybean sprouts. In addition to the yields, nutrients, and antioxidant potentials considered in the previous study [
32], the present study compares the color values and isoflavone content of soybean sprouts produced by treating seeds with persimmon fruit powder and that of INB-treated sprouts.
4. Conclusions
This study investigated the effects of Indolbi and persimmon fruit powder on the yield and nutritional values of soybean sprouts. The results of the present study showed that soaking soybean seeds in water containing persimmon fruit powder or applying Indolbi can significantly increase the yield, vitamin C, free amino acids, minerals, isoflavones, and total phenolic contents of soybean sprouts. Based on the yield and nutritional parameters investigated in the present study, the effect of persimmon fruit powder, especially at 2.5% (w/v) in the water, was superior compared to that of Indolbi. Moreover, because of potential health hazards, the use of synthetic chemicals like Indolbi is less preferred than that of natural products by consumers, therefore, persimmon fruit powder could be a good option to enhance the yield and nutritional value of soybean sprouts.