The Production And Prevention Of Macadamia Off-flavor During Storage

Macadamia nuts are rich in sugar,lipid and protein,as well a good source of nutrition and energy.Currently,primary processed products such as roasted open shell macadamia nuts are the main macadamia products in China,and their demand and production have continued to increase.However,it is difficult to maintain the quality and the products often produces offflavor and there are often occur quality deterioration during long-term storage,which greatly limits the development of macadamia industry.Thus,in our article,roasted open shell macadamia products during storage at room temperature were selected as the research objects to find out the composition and cause of off-flavor by analyzing the changes in odor and nutritional composition.On the basis of the above research,corresponding measures were taken from processing and packaging to prevent and control the generation of off-flavor of macadamia products.The main research contents and results of this subject are as follows:1.Roasted open shell macadamia products stored for 0,3,6,and 9 months were selected as the research objects to analyze the odor profiles of samples by the sensory odor attribute scoring and fast gas-phase electronic nose,as well as to obtain the composition and contents of volatiles and odor characters of samples by HS-SPME/GC-MS technology,relative odor activity value(ROAV)method and partial least square regression(PLSR)analysis method.The results showed that the odor quality of macadamia nuts decreased with storage time.Besides,nonanal,octanal,hexanal,heptanal,trans-2-octenal,trans-2-nonenal,trans-2-decenal,decanal,(E)-2-heptenal,valeraldehyde and hexanoic acid are the key components that have an important contribution to the unpleasant odors of macadamia nuts.2.The changes of nutrients,such as protein,amino acids,total sugar,reducing sugar,total lipid,fatty acid,as well as the corresponding changes in physicochemical indicators were analyzed to deeply explore the reasons of unpleasant odors of macadamia products after storage.The results showed that there were only slight differences in the protein and amino acid contents,and there were no significant chemical reactions in sugars,while the total lipid and total fatty acid contents decreased by 6.35 g/100 g db and 137.46 mg/g,respectively,with the prolongation of storage time.The acid value(AV),peroxide value(PV),anisidine value(p-An V)and total oxidation value(TOTOX)of oil also increased significantly during storage,with the increments of 1.89 mg/g,3.99 mmol/kg,2.82 and 19.08,respectively.Therefore,the off-flavor of macadamia products during storage are mainly caused by lipid oxidation.Moreover,the analysis of physicochemical indexes and microscopic during processing showed that thermal processing was an important cause of the lipid oxidation.3.The lipid oxidation of macadamia nuts was inhabited by different packaging methods,such as vacuum-added deoxidizer package,nitrogen-added deoxidizer package and replacement deoxidizer package.Combined with the regression equation ln(T)=-0.0045s+4.7432 of shelf-life,it was calculated that the shelf-life extension rates of the above packaging methods were 28.25%,7.93% and 13.35%,respectively,and the vacuum-added deoxidizer package had the best inhibitory effect on lipid oxidation of macadamia products.4.The lipid oxidation of macadamia nuts was inhabited by adding TBHQ before roasting.The problems such as poor solubility and uneven addition of TBHQ were solved by adding glycerol,citric acid fatty acid glyceride and sorbitol.The additives were found to increase the penetration of TBHQ in macadamia nuts,so that they can enhance the antioxidant capacity of nuts.Among them,citric acid fatty acid glyceride was the most effective penetrant.Interestingly,it was found that when the addition of TBHQ is fixed,the permeation of TBHQ first increased with the penetrant,and when the penetrant amount reached a certain value,the permeation amount of TBHQ did not increase but decreased with the penetrant.In addition,when the dosage of TBHQ decreased,it was found that the increment of the permeation amount of TBHQ decreased gradually,so did the increment of OSI and DPPH free radical scavenging ability.It can be seen that the effect of penetrant also has a certain dose-effect relationship with the addition amount of TBHQ.