Effect of some fermentation factors on the fermented tiger stripe peanut production by Rhizopus microsporus fungus

Abstract

Tiger stripe peanut (Arachis hypogaea L.) (TSP) is a famous Thailand geographical indication (GI) product of the Mae Hong Son province, Thailand.  However, the value-added products of this peanut have been required by many local entrepreneurs. Therefore, the production of fermented TSP, a Tempe-like product, by Rhizopus microsporus fungus was proposed in our research. The objectives of this study were to investigate the effects of inoculum size (10⁵, 10⁶, and 10⁷ spores/g), incubation temperature (25, 30, 35, and 40^oC), and fermentation time (1-7 days) on the soluble reducing sugar, available phosphate and soluble protein of fermented TSP. Subsequently, some chemical properties of the product were studied. The results showed optimal fermentation conditions included an inoculation size of 10⁷ spores/g and incubation at 35^oC for two days. Moreover, the results from the proximate analysis study demonstrated that the crude protein content of fermented TSP increased by approximately 17% (by DW). The fat, carbohydrate, and crude fiber contents decreased by 3.5, 5.9, and 4.2% (by DW) compared to unfermented TSP, while their calculated energy contents were between 538-539 kcal/100 g DM. Total phenolic content (gallic acid equivalent, mg/g DW) and ABTS (2,2ʹ-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid)) scavenging antioxidant capacity (Trolox equivalent, mg/g DW) of TSP were enhanced by approximately 2.6 and 1.9 folds, respectively, after fungal fermentation. Overall, the fermented TSP obtained from these optimized processes will be a new nutritious food product. However, further study on its health benefits will be able to apply this product as a novel functional Thai food.