| The peanut processing products mainly includes peanut oil,snack food,peanut butter and vinegar-soaked peanuts.Roasting is the most common processing method in peanut processing,which can be used to produce aroma and remove red coat.Vinegar-soaked peanuts are a traditional functional food in China,but the mechanism of biochemical reactions that occur during the vinegar-soaked process of peanuts is not clear.Our laboratory had previously confirmed that peanuts contain endogenous proteases,which had strong hydrolytic activity under acidic conditions(p H 3～p H 5),so they could be used as dietary proteases(to aid digestion)and could also be used to modify proteins during processing.Based on this,this paper will systematically study the properties and applications of endogenous proteases in peanut processing(roasting,vinegar-soaking),and explore the activities and applications of endogenous proteases in different peanut varieties.The main research contents and results are as follows:Firstly,the contents of lipids and proteins,extraction rates and endogenous proteases activity of five peanut varieties were compared.The results showed that the contents of lipids(46.95%～51.35%)and proteins(24.66%～29.68%)were different among varieties.The extraction rates of protein of different peanut varieties(91.86%～97.77%;highest with Luohanguo,lowest with Huayu)had obvious influence,but had little influence on the lipid extraction rates(about 98%).There were differences in endogenous protease activities among peanut varieties,but the endopeptidase of all varieties showed the strongest activity at p H 3.Exopeptidase activity of all varieties increased with the increase of p H,and Sililong was the highest and Huayu was the lowest at p H 5.As for the synergistic activity of endopeptidase and exopeptidase,the Huayu was the strongest at p H 3,while the other four varieties were the strongest at p H 5.Then,the effects of roasting(50°C～140°C,1 h)on the quality of oils,protein properties and endogenous protease activities in peanuts were investigated.The results showed that the acid value increased with the increase of roasting temperature,and the peroxide value showed a trend of rising first and then falling,but it did not exceed the national standard.Moderate roasting can improve the protein extraction rate,up to 98.78%(120°C);PDI with the increase of roasting temperature showed a first up and then descend trend,the highest was 98.73% at90°C;when roasting temperature ≤ 110°C,PDI exceeded 95%.The degree of hydrolysis of peanut protein by endogenous protease increased at first and then decreased with the increase of roasting temperature.When roasting temperature was ≤ 110°C,roasting was beneficial for the hydrolysis of peanut protein by endogenous proteases,and peanut protein was most easily hydrolyzed at 70°C～80°C;when the roasting temperature was 120°C～140°C,roasting was not beneficial for the hydrolysis of peanut protein by endogenous proteases;endogenous proteases still had activity at 140°C to some extent,which indicates that endogenous proteases in peanut seeds had thermal stability.Finally,the degradation and release of protein in vinegar-soaked peanuts were investigated,the relationship between protein degradation and endogenous proteases was confirmed,and the quality of oil in vinegar-soaked peanut was explored.According to the traditional method of soaking peanuts with vinegar,the system of peanut: vinegar = 5: 8(w/w)was soaked at room temperature(25℃)for one week,and the vinegar-soaked peanuts and vinegar-soaked liquid were separated and analyzed respectively.Peanuts included raw peanuts and roasted peanuts(110℃,1 h),and vinegar included white vinegar(crude protein content 0.04%)and black vinegar(crude protein content 3.68%).The results showed that under the condition of white vinegar,the TCA-NSI of protein components in vinegar-soaked raw peanuts was 7.43%(compared with 2.94% of original peanuts),and the allergen protein Ara h 1 was almost completely degraded.The protein content of vinegar-soaked liquids was 1.75%,and the protein components included proteins(3 k Da～30 k Da),peptides and free amino acid(0.30 g/100 m L).Under the soaking condition of black vinegar,the TCA-NSI of protein components in vinegarsoaked raw peanuts was 12.97%,and the degradation of Ara h 1 was almost complete.The protein content of acid-soaked liquids was 4.72%,and the protein species(5 k Da～30 k Da)were more than those of white vinegar,and it also contained peptides and free amino acid(1.41g/100 m L).The p H of two kinds of vinegar-soaked liquids and two kinds of vinegar-soaked peanuts were in the range of 3.76～3.97,which was the optimum p H for endogenous proteases activity,indicating that the degradation of peanut proteins during vinegar soaking should be induced by the hydrolysis of endogenous protease.For the endogenous protease in vinegarsoaked peanuts,it still kept high activity,and it was easier to degrade the remaining globulin in vinegar-soaked peanuts,which indicated that endogenous proteases had acid stability,and vinegar-soaked peanuts made peanut proteins easier to be degraded by enzymes.For roasted peanuts(110℃,1 h),endogenous proteases could still hydrolyze peanut proteins under vinegar soaking condition,but the degree of hydrolysis was lower than that of raw peanuts.After the soaked peanuts was dried at low temperature,it was pressed to make oil.The results showed that the peroxide value of peanut oil treated with black vinegar(0.52 mmol/kg)was much lower than that treated with white vinegar(3.70 mmol/kg),while that of the control peanut oil was0.34 mmol/kg,indicating that compared with white vinegar,soaking with black vinegar could significantly slow down the increase of peroxide value.Roasted peanuts showed a similar trend,but the peroxide value increased(white vinegar,4.64 mmol/kg;black vinegar,0.91 mmol/kg). |
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