Effects Of Storage Temperatures On The Quality And Shelf Life Of Skim Fresh Milk

Defatted dairy products are favored by people with low-fat diet demand,but the potential impact of temperature fluctuations caused by transportation,sales and storage during the shelf life on quality still needs to be further studied.In this study,commercially available low-temperature defatted fresh milk(15 days shelf life)was used as the research object,and stored at 4℃,15℃,25℃ and 30℃ for 21 days,respectively.The sensory score,physical and chemical analysis,total number of colonies,electronic tongue,electronic nose and volatile flavor substances were measured.Furthermore,the correlation analysis of detection indexes,temperature and storage time was carried out,and the shelf life equation was calculated according to the key change indexes,so as to predict the quality of skimmed fresh milk during the shelf life.The main results are as follows:(1)Under the condition of 4℃,there was no significant change in the quality index of the samples within 21 days.Under the condition of 15℃,the product was relatively stable,but the contents of furosine and total bacterial count increased significantly(P<0.05),the sensory score decreased significantly,and the sensory requirements met the national standard within 10 days.Under the conditions of 25℃ and 30℃,the quality changed significantly after 7 days of storage.The titratable acidity,furosine and total bacterial count increased significantly,and the sensory score decreased significantly.After 7 days,the sensory requirements did not meet the national standard.(2)With the increase of storage temperature and storage time,the odor distance of the electronic nose and the distance between the ED value of the electronic tongue and the initial state of the sample showed a significant upward trend.The electronic nose and the electronic tongue can effectively distinguish the flavor differences caused by storage temperature and time.The detection results of volatile flavor substances showed that a total of 50 flavor substances were identified at 4 different storage temperatures,mainly aldehydes,ketones,acids,alcohols and sulfur-containing compounds.Among them,aldehydes and acids were greatly affected by temperature.With the increase of temperature,aldehydes decreased and acids increased,which indicated that the changes of aldehydes and acids may be the key factors causing flavor changes.Among them,hexanal in aldehyde compounds is greatly affected by temperature,which is the key flavor substance for the flavor change of skim milk.(3)The Arrhenius equation of shelf life was calculated for different detection indexes.Among them,the titration acidity can be used as a calculation index.The relative error between the predicted days of storage period and the actual days of storage was less than 10.24%,which indicated that the prediction equation calculated by the titration acidity index could be used to predict the shelf life of defatted fresh milk.In summary,the furosine,titratable acidity,sensory score and volatile flavor substances of defatted fresh milk during shelf life may be affected by storage temperature,but low temperature has little effect.This study provides data support for industrial production of skimmed fresh milk,and provides guidance for dealers to store and transport reasonably and consumers to drink skimmed fresh milk products correctly.