| Cashew nut,hazelnut,walnut and almond are recognized as the four great nuts in the world.Cashew nuts are good food resource that contain plenty of lipids and proteins and other nutrients.However,cashew nut may possibly arouse the allergen reaction in human body.Heating treatments are commonly applied for nuts processing.Different types of heating treatment will make different influence on the nutrients and flavor of nuts.What's more,intense heating treatments may change the allergen of nuts.In order to explore the effect of heating treatment on cashew nut,three processing ways boiling,roasting,frying were selected.The content of protein,amino acids,lipid,carbohydrates and polyphenols were detected and compared in processed cashew nuts and raw nut.Roasting and frying were selected to investigate the allergen changes after heating.Further researches have been done on the changes of allergen in different processed cashew nuts after in vitro digestion.Findings are listed as below:(1)In raw nut,21% of protein,18.3% of total amino acids,47% of fat with eighty percent of unsaturated fatty acids,6.4% of amylose and 2.8% of amylopectin,4.5% of sucrose,8‰ of both glucose and fructose,2.1‰ of total phenols and 0.27‰ of flavonoids have been detected.The mean energetic value is 2170 kJ/100 g.After heating treatments,the content of total amino acids,sucrose,fructose,total phenols and flavonoids decreased significantly(p<0.05).However,the content of starch showed a significant increase in roasted nuts(p<0.05),but a decrease in fried and boiled nuts(p<0.05).The content of lipids increased significantly in fried nuts(p<0.05),but decreased significantly in boiled and roasted nuts(p<0.05).The content of glucose significantly increased in boiled nuts(p<0.05),but decreased in roasted and fried nuts(p<0.05).Mean energetic values of different processed cashew nuts showed the order of fried nuts>raw nuts>boiled nuts>roasted nuts.Taking all the changes of the nutrients and the mean energetic value of cashew nuts into account,we concluded that boiling was the better way to preserve the nutrients of cashew nut.(2)Eighteen types of volatile compounds have been detected in raw cashew nut in which hydrocarbons and aldehydes contributed most to the flavor.The relative content of hydrocarbons and aldehydes were 27.46% and 20.42% respectively.After heating treatment,the flavor composition of cashew nut changed.Nineteen types of volatile compounds have been detected in boiled nuts in which aldehydes and hydrocarbons contributed most to the flavor.The relative content of aldehydes and hydrocarbons were 48.7% and 31.43% respectively.It was obvious that the relative content of aldehydes was greater than raw nuts.So,the formation of flavor should be related to lipids oxidation.Thirty-four types of volatiles were detected in roasted cashew nut in which pyrazines and aldehydes contributed most to the flavor.The relative content of pyrazines and aldehydes were 37.96% and 15.09% respectively.Besides,4.1% of furfuran had also been detected.It should be concluded that the composition of flavors in roasted nuts were most related to Maillard reaction,Lipids oxidation and Caramelization reaction.Thirty types of volatiles were detected in fried nut which only yielded to roasted nut.The relative content of pyrazines and aldehydes were 39.45% and 26.9% respectively.It should be concluded that the composition of flavors in fried nuts were most related to Maillard reaction and Lipids oxidation.In conclusion,roasted and fried nuts were abundant in pyrazines and had good flavor.Both of them were good processing methods.(3)Compared with raw cashew nut: The content of soluble protein showed no significant difference in cashew nut roasted for 8 min(p>0.05),the content of trichloroacetic acid(TCA)soluble peptides increased significantly(p<0.05),the relative content of random coil increased but the difference was not significant(p>0.05);while in cashew nuts roasted 12 min,a significant decrease and increase were found in the content of soluble protein and relative content of random coil respectively(p<0.05),but the content of TCA soluble peptides was not significant changed(p>0.05);In cashew nuts roasted 16 min,the content of soluble protein and relative content of TCA soluble peptides decreased significantly(p<0.05),the relative content of random coil increased significantly(p<0.05).After heating,the allergenicity of per gram protein enhanced significantly(p<0.05)in 8 min and 12 min roasted nuts.While in 16 min roasted nuts,no obvious difference was found.With the extension of roasting time,the content of soluble protein and TCA soluble peptides decreased gradually.The relative content of random coil increased and the protein structure tended to be more disordered.The allergenicity of per gram protein showed a decrease trend.The results showed that allergenicity of cashew nut was related to the solubility and structure of protein,while all these were affected by roasting time.In fried nuts,the content of soluble protein and relative content of TCA soluble peptides decreased significantly(p<0.05),the relative content of random coil increased significantly(p<0.05),however,the allergenicity of per gram protein enhanced significantly(p<0.05).It should be concluded that heating with short time and high temperature may enhance the allergenicity of cashew nuts.(4)After in vitro digestion,the IgE binding capacity of per gram protein showed a great reduction in raw and heated cashew nuts.It indicated that the protease hydrolysis had an excellent effect on reducing cashew protein allergenicity.Besides,the IgE binding capacity of per gram protein in fried nuts was significantly lower than raw nuts protein(p<0.05).While no obvious difference was found between roasted nuts and raw nuts.The results of digestibility indicated that the protein in fried nuts was easier to be digested than in raw nuts.The protein digestibility of roasted nuts was the smallest.It should be noted that less content of protein was detected in digestive juice of roasted and fried nuts than of raw nuts.So it could be concluded that the IgE binding capacity of per gram protein could be reduced by in vitro digestion,and the total allergenicity of digestive juice in heated nuts is less than in raw nuts.Thus,we speculated that frying and roasting will benefit to reduce the allergen reaction to cashew nuts. |
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