| Peony seed meal is rich in proteins,carbohydrates and bioactive substances,which is an ideal resources of plant proteins and bioactive substances.However,there were few studies on the efficient utilization of peony seed meal.It has certain research significance for producing soy sauce by replacing soybean with peony seed meal,which could reduce the cost of soy sauce production and the waste of resources from peony seed meal,as well as enhance the antioxidant activity of soy sauce products.In this study,the conditions of making soy sauce koji from peony seed meal were optimized.The physicochemical properties,flavor and taste characteristics as well as antioxidant activities of peony seed meal soy sauces fermented by low-salt solid-state and high-salt dilute-state fermentation processes were investigated.The results were as follows:(1)The koji-making conditions of water content,culture time,culture temperature and raw material ratio(mixture of peony seed meal and soybean meal: bran,g:g)were optimized by single-factor experiment and response surface method.All the optimization experiments were evaluated using neutral protease activity as the index.The results showed that the optimum conditions were 46.1% of water content,48.6 h of culture time,31.5℃ of culture temperature and 2.1:1 of raw material ratio.The maximum neutral protease activity of koji prepared with these conditions was 2193.78U/g.(2)The low-salt solid-state peony seed meal soy sauce at 20 d of fermentation and the high-salt dilute-state peony seed meal soy sauce at 120 d had the highest contents of amino acid nitrogen and soluble salt-free solids.Their qualities were better than peony seed meal soy sauces at other fermentation periods.The total nitrogen,amino acid nitrogen and soluble salt-free solids contents of the high-salt dilute-state peony seed meal soy sauce at 120 d of fermentation were 1.4845 g/100 m L,0.7724 g/100 m L and20.96 g/100 m L,respectively.These values were significantly higher than those of the low-salt solid-state peony seed meal soy sauce at 20 d of fermentation(1.4633 g/100 m L,0.7319 g/100 m L and 18.53 g/100 m L,P<0.05).Both low-salt solid-state peony seed meal soy sauce and high-salt dilute-state peony seed meal soy sauce met the requirements of the Chinese national standard for first-grade soy sauce.(3)A total of 65 volatile flavor substances were detected in the high-salt dilute-state peony seed meal soy sauce.Alcohols and esters were the main substances,accounting for 32.76% and 27.13% of the total volatile flavor substances.59 kinds of volatile flavor substances were detected in low-salt solid-state peony seed meal soy sauce.Acids and aldehydes were the main substances,accounting for 23.11% and22.28% of the total volatile flavor substances.In addition,the umami and sweet amino acid contents of high-salt dilute-state peony seed meal soy sauce reached 1755.83 g/100 m L and 1489.59 g/100 m L.These values were significantly higher than those of low-salt solid-state peony seed meal soy sauce(1651.84 g/100 m L and 1231.61 g/100 m L,P<0.05).Among the two peony seed meal soy sauces,high-salt dilute-state peony seed meal soy sauce had stronger mellow,floral and fruity aromas.It also had more sweet and umami taste,as well as better color.Compared with soybean meal soy sauces,peony seed meal soy sauces had more types of volatile flavor substances and higher sweet amino acids content,resulting in a stronger floral,fruit aromas and a sweeter taste.In addition,peony seed meal soy sauces had a deeper reddish-yellow hue.(4)High-salt dilute-state peony seed meal soy sauce had significantly higher total phenolic and total flavonoid contents(571.73 mg GAE/100 m L,87.78 mg RE/100 m L)than low-salt solid-state peony seed meal soy sauce(516.77 mg GAE/100 m L,76.05 mg RE/100 m L,P < 0.05).The DPPH radical scavenging power,ABTS radical scavenging power and reducing power of high-salt dilute-state peony seed meal soy sauce were 75.79%,180.25 mmol Trolox/m L and 6577.60 μg AAE/m L,respectively.These values were significantly higher than low-salt solid-state peony seed meal soy sauce(75.57%,169.17 mmol Trolox/m L,6039.58 μg AAE/m L,P<0.05).In addition,the in-vivo oxidative damage protection of high-salt dilute-state peony seed meal soy sauce(T-AOC value of 0.2725 mmol/g prot,SOD activity of 4.5168 U/mg prot and CAT activity of 0.9421 U/mg prot at 0.5% concentration)were also significantly stronger than low-salt solid-state peony seed meal soy sauce(0.2632 mmol/g prot,4.4126 U/mg prot,0.8876 U/mg prot,P < 0.05).Compared with soybean meal soy sauce,peony seed meal soy sauce had higher total phenol and total flavonoid contents and better in vitro antioxidant activities,as well as in vivo antioxidant activities. |
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