Effect Of Milk Composition On Sensory Quality Of Coffee And Its Related Mechanism Analysis

Coffee was one of the three most popular drinks in the world,its sales in China had grown rapidly in recent years.However,previous studies on coffee mainly focused on the influence of coffee varieties and processing on black coffee,which deviates from the current situation that Chinese consumers mainly consume white coffee.The composition of milk was often altered in milky coffee.Therefore,understanding the law and related mechanism of the influence of milk composition on coffee flavor was of great importance for the development of China's coffee industry.In this research,based on the sensory attributes that drove the liking of Chinese consumers,the influence of non-fat milk solids(MSNF)and milk fat in milk on the sensory attributes of coffee with different roasting degrees were studied,and the chemical mechanism of the effect of milk composition on the sensory characteristics of coffee was also discussed from the perspective of the change of the release characteristics of related flavor compounds.The main research contents and results were as follows:Analysis of drivers of liking for white coffee: An online questionnaire survey of 724 milk coffee consumers showed that the drivers of liking for consumers to drink white coffee was its sensory characteristics.From different dimensions,the importance of aroma,taste and taste decreased in turn.Further,9-point hedonic tests and Check-All-That-Apply tests(CATA)on 194 consumers were conducted with five commercial milk coffees.According to penalty-lift analysis,the key aroma attributes of driver of liking were milk flavor,coffee flavor and caramel flavor,while the existence of smoky and burnt flavour would reduce consumers' acceptance.In addition,smoothness and sweetness of white coffee can significantly improve consumer acceptance,while bitterness can inhibit consumer acceptance.Furthermore,similar results were obtained by using external preference diagram analysisInfluence of milk components on white coffee:(1)In this research,quantitative descriptive analysis was used to compare coffees with different MSNF and milk fats,and the differences in the effects of coffee with different roasting degrees were also considered.The results showed that both MSNF and milk fat would significantly reduce the most attributes from black coffee(e.g.smoky and burnt).But for green and roast flavor,MSNF had an enhanced effect,and milk fat had the opposite effect.Coffee with different roasting degrees had the same tendency to be affected by milk composition,but the degree of influence was different.As a result,MSNF would amplify the sensory differences of samples with different roasting degrees,while milk fat would reduce the sensory differences between samples.Overall,both MSNF and milk fat would improve the flavor of coffee in a direction that improve consumer acceptance.(2)Dynamic changes of single drink: The results of temporal dominant snesation(TDS)evaluation showed that MSNF enhanced the level of flavor changes(burnt milk flavor and sweet taste)during the drinking process of milk coffee,while the addition of milk fat eliminated some negative attributes(such as paste tobacco taste)of black coffee,and made the milk flavor dominant.(3)The dynamic changes of the continuous drinking: according to the result of multi-sip TDS,compared with one sip of drinking coffee,continuous drinking did not significantly change the overall feeling of coffee.However,after continuous drinking,MSNF would gradually enhance the bitter taste after swallow,which was not conducive to consumer acceptance,and milk fats would gradually weaken the milk flavor which promotes consumer acceptances,and gradually enhance the burnt flavor.In other words,while both componates contributed to the improvement in coffee flavor,continuous drinking may weaken this effect.Influence mechanism of milk componates on the release of key flavor substances and sensory expression in coffee:(1)The influence on unbound taste componate and related mechanism.The determination of unbound caffeine,chlorogenic acid,organic acid and free hydrogen ion content showed that MSNF can be combined with a small amount of chlorogenic acid which contribute to sourness and bitterness,and can reduce the free hydrogen related to sourness.Milk fat had no effect on the content unbound componate in the solution.All the above phenomena were not consistent with the trend that the bitterness and sourness of coffee was gradually decreased by MSNF and milk fat.Therefore,it was speculated that the interaction between milk components and taste receptors was another reason that milk affects the taste of coffee(2)Influence on the release of volatile componates and related mechanism.The release rate of volatile components in white coffee were compared.The results showed that,on the one hand,MSNF and milk fat can affect the release of volatile substances in coffee,which was due to the binding and repulsive action of whey protein and casein in MSNF and the salting-out of lactose and salt.As a consequence,the release of 6 compounds were reduced and 12 compounds were promoted.Milk fat inhibited the release of 62 volatile componates due to its retention of hydrophobic components.On the other hand,the addition of non-fat milk solids or milk fats in milk can introduce volatile components in milk.The introduction of milk increased decanoic acid,2-heptylone,2-nonone and 2-Undecanone in coffee.(3)The relationship between odor active components and sensory performance.Using GC-O,48 aroma-active componates with significant changes in headspace concentration affected by MSNF or milk fat were identified.PLSR was used to establish a good relationship between odorous active components and coffee aroma.The goodness of fit of the model reached 0.613 951 and 0.954 in light,medium and dark roast coffee,respectively.According to the PLSR analysis,21 components were positively correlated with the smoky and sourness of coffee,4 of them were affected by MSNF,and 21 were significantly affected by milk fat.28 componates were related to roast flavor,including 7 componated influenced by MSNF,25 significantly affected by the milk fat.Three compounds were positively correlated with milk aroma,all of which originated from milk itself and increased with the increase of MSNF and milk fat.