Preparation of soy sauce by walnut meal fermentation: Composition, antioxidant properties, and angiotensin‐converting enzyme inhibitory activities

Abstract

Remaining walnut meal after oil extraction still contains many nutrients. However, these by‐products have not been effectively used. In this study, walnut meal and Aspergillus oryzae (3.042) were used in combination to prepare a soy sauce‐like material with high amino nitrogen content (ANC). The optimal conditions for the preparation of walnut soy sauce (ratio of brine:koji of 1.7:1 for 6 days at 45°C) were determined using response surface experiments (RSE), which showed maximum ANC of 855 mg/100 ml. The results of amino acid analysis indicated that walnut soy sauce had a similar amino acid composition compared with three commercial soy sauces. It contained all the essential amino acids and had a high content of umami amino acids such as Glu and Asp, which may give it a stronger umami taste. Moreover, the crude walnut soy sauce was extracted sequentially using ethyl acetate, n‐butanol, acetone and water, and the total phenols, total flavonoids, reducing sugars, and the peptides of different solvent extracts were measured. Results showed that the total phenolic and flavonoid contents were highest in the ethyl acetate extracts. However, water residue had the highest levels of reducing sugars and peptides. In vitro, the water residue showed the highest antioxidant capacity and angiotensin‐converting enzyme (ACE) inhibitory activity, due to more reducing sugars and peptides. These results indicated that walnut soy sauce may have significant antioxidant and ACE inhibitory activity. The findings provide a scientific basis for developing a replacement for soy sauce and broaden the beneficial application of walnut meal.

Recent progress and advances in soy sauce production technologies: A review

“…Studies have shown that soy sauce prepared using raw soybean extrusion pretreatment has higher levels of total amino F I G U R E 1 The transition of soy sauce from a food condiment to a potential functional food F I G U R E 2 Feedstock for soy sauce production nitrogen content, free amino acids (FAAs), sugar reduction, and protein utilization than conventional raw materials. Moreover, defatted soy flour fermented using halophilic bacteria without the addition of dried fermented soybeans (meju) to prepare soy sauce and the quality of the directly fermented soy sauce using defatted soy flour was found to be better than that prepared using meju (Xu et al, 2020). Soy sauce-like seasonings have also been introduced recently to fulfill consumer demands.…”

“…Soy sauce-like seasonings have also been introduced recently to fulfill consumer demands. These alternative soy sauces substitute soy sauce and wheat with different kinds of beans or grains, such as peas or broad beans, rice, quinoa or foxtail millet, as raw materials (Yamana et al, 2020), and by-products such as walnut meal (Xu et al, 2020) and okara (Lee et al, 2020). Detailed metabolomic analysis of these soy sauce-like seasonings made from different feedstock characteristic compounds and umami revealed that grain-based samples have a higher saccharide content and umami taste, whereas bean-based samples have a higher amino acid content (Yamana et al, 2020).…”

“…Detailed metabolomic analysis of these soy sauce-like seasonings made from different feedstock characteristic compounds and umami revealed that grain-based samples have a higher saccharide content and umami taste, whereas bean-based samples have a higher amino acid content (Yamana et al, 2020). Additionally, Xu et al (2020) investigated the use of the remaining walnut meal after oil extraction as a potential lowvalue raw material for the preparation of soy sauce-like products.…”

The microbial community, biogenic amines content of soybean paste, and the degradation of biogenic amines by Lactobacillus plantarum HM24

“…Soybeans were crushed after high-pressure steaming for 20 min, and koji was made naturally in the laboratory environment for two months. The koji was ground and put into water containing 8% sea salt, and mixed koji and brine in the ratio of 1:1 (Xu et al, 2020).…”

Antioxidant Peptides from Sepia esculenta Hydrolyzate Attenuate Oxidative Stress and Fat Accumulation in Caenorhabditis elegans

“…There is growing interest in the therapeutic applications of food-derived bioactive substances as safer alternatives, either as nutraceuticals or functional foods [ 11 , 12 , 13 ]. Bioactive peptides are a class of multifunctional compounds derived from food proteins, which have been reported to possess a variety of important physiologically related biological activities such as antioxidant, antihypertensive, and anti-inflammatory actions [ 14 , 15 , 16 ].…”