From Coconut Pulp To Coconut Milk:Study On Quality Changes

Fresh coconut pulp is widely used for the primary ingredients in the various products,while the flavor and quality of fresh coconut pulp after squeezing are easily change.Moreover,sterilization is an important process in beverage production that not only guarantees the edible safety of beverage but also extends its shelf life.However,the quality changes in the coconut milk before and after sterilization has received scarce attention in regard to beverages.At present,the shelf life of coconut milk has different time(3 months,6 months,9 months and 12 months,etc.),but there is unclearly report on the quality change of coconut milk during the shelf life(12 months).Therefore,in this work,fresh coconut pulp and coconut milk are the mainly research object.The changes of volatile compounds in fresh coconut pulp after squeezing(for 2-12hours)were studied.This study was also conducted to investigate the effect of sterilization(at 121? for 30 min.)and after sterilization(from day 1 to day 19)on the physicochemical properties,volatile compounds,free fatty acids and sensory properties of coconut milk.The changes in physicochemical properties,volatile compounds,free fatty acids,free amino acids and sensory properties of coconut milk during shelf life(12 months).The results are as follows:(1)Changes of volatile components in fresh coconut pulp after squeezingIn this study,the volatile compositions of fresh coconut pulp squeezed at ambient temperature for 2-12 hours was investigated by headspace solid-phase microextraction with gas chromatography–mass spectrometry and multivariate data analysis.A total of 36 compounds were identified.The principal component analysis and partial least squaresdiscriminant analysis result demonstrated distinct separations between 2 hours,4 hours,6hours and 8-12 hours,indicating significant compound changes in fresh coconut pulp.After orthogonal partial least squares-discriminant analysis,totally five flavor compounds are identified contributed to the discrimination between 2-4 hours and 6-12 hours,including 3-hydroxy-2-butanone,2-heptanol,butanoic acid,acetic acid and propanoic acid.The pathway analysis results indicated that acetic acid is closely related to sulfur metabolism and pyruvate metabolism.Moreover,the percentage of acetic acid significantly increased from 0.40% to 44.33% for 2-12 hours.In conclusion,these results indicate that the quality of fresh coconut pulp remarkably changed after squeezing;moreover,metabolomics could become a potential evaluation method to objectively evaluate the changes of the quality of fresh coconut pulp after squeezing.(2)Effects of sterilization on the quality of coconut milkThe single-factor experiment confirmed that the extraction conditions of headspace solid-phase microextraction were as follows: the amount of coconut milk was 5m L,the concentration of Na Cl was 30%,the extraction temperature was 60?,the equilibrium time was 30 min and the adsorption time was 40 min.The volatile compounds present in coconut milk were determined by solid-phase microextraction and gas chromatography-mass spectrometry.A total of 31 volatile compounds in coconut milk were tentatively identified,including lactones(34.4%),esters(31.5%),aldehydes(20.0%),acids(3.8%),ketones(2.3%),alcohols(1.4%)and other(0.6%).The relative content of delta-octalactone in lactones had no significant change after sterilization compared with nontreatment,while an increase was observed in the relative content of delta-octalactone from 18.14% to 23.81% in storage.In addition,although the percentage of ethyl octanoate(from 13.15% to 9.05%)in esters significantly decreased after sterilization compared with nontreatment,the content had no significant alter during storage.Those results showed that the volatile compounds in coconut milk changed after sterilization and storage.Further analysis with descriptive sensory evaluation showed that the sensory evaluation ranged from the moderate to extreme levels according to the evaluators.This result indicated that no remarkable change in the sensory qualities of coconut milk by sterilizing and storing.Meanwhile,all attributes had a positive effect on coconut milk,such as overall coconut milk flavor,sweet,nutty.There is no conspicuous affect in the acceptability of coconut milk by evaluators.The free fatty acid present in coconut milk were determined by solid phase extraction and gas chromatography.The results showed that the free fatty acids in coconut milk did not change significantly after sterilization and storage.Overall,these results indicate that sterilization had no significant affect the flavor of coconut milk;moreover,appropriate storage can improve the acceptability of coconut milk before product shipment.(3)Quality changes in coconut milk during shelf lifeThe physicochemical properties,volatile components,free fatty acids,free amino acids and sensory properties of coconut milk were significantly changed during the shelf life(12months)at ambient temperature.The conductivity,soluble solids and p H value of coconut milk did not change significantly,L value gradually decreased,a value and b value first increased and then decreased,and the acid value gradually increased during shelf life.A total of 29 volatile components,24 free amino acids and 7 free fatty acids were identified in coconut milk,respectively.The volatile components in coconutmilk,such as 2-hexanone,octanal,hexanal,ethyl octanoate and ethyl laurate,altered obviously.During shelf life,the umami glutamate in coconut milk decreased significantly from 8 months,and the sweet alanine decreased significantly from 7 months.The relative contents of octanoic acid,palmitic acid and stearic acid in coconut milk showed a decreasing trend,the relative contents of lauric acid had no significant change,and the relative contents of decanoic acid had no significant change,except for a significant increase for 2 months.The relative content of myristic acid and oleic acid increased.The sensory evaluators' preference for coconut milk decreased gradually during shelf life,while the strongly preference for coconut milk stored at 2 and 5 months.Overall,the quality of coconut milk changes as shelf life time increases.