Study On Fermentation Technology And Textural Properties And Flavor Components Of Purple Sweet Potato Set-style Yoghurt

Purple sweet potato yoghurt is a kind of nourishment contains both the nutrients ofyoghurt and the health benefits of purple sweet potato, it has unique flavors as well asattractive color, and the market prospect of this kind of yoghurt is bright.This paper optimized the fermentation process conditions of purple sweet potatoyogurt. Its textural properties were studied by texture technology, flavor components werestudied by headspace solid-phase micro-extraction (HS-SPME) coupled with gaschromatography-mass spectrometry (GC-MS). An elementary research about thecorrelation between the sensory evaluation parameters and the instrumental measurementparameters was done.The contents and results of this study were shown as follows:1. The TPA experiments were tested on set-style purple sweet potato yoghurt, thedegree of the deformation and the compression speed were selected as research object.The influence was analyzed by response surface methodology. Results showed that thesetextural parameters were mainly depending on the degree of deformation, while theinfluence of the speed of compression was less. The ideal conditions were: degree of thedeformation (120mm/min) and compression speed (37.5%).2. The fermentation process conditions of purple sweet potato yoghurt wereoptimized by response surface methodology. The optimal parameters were shown asfollows: fermentation temperature was42℃, sugar amounts was3.3%, inoculationnumbers was3%, the ratio of milk powder and purple sweet potato flour was14:1. Theyogurt had smooth structure, good taste and excellent flavor.3. Influences of different fermentation process conditions of textural properties ofpurple sweet potato yoghurt were studied. Results showed that there was a positivecorrelation between the added amount of sugar and the texture properties of purple sweetpotato yogurt, except the springiness of it. And with the increase of inoculation numbers,the texture properties first increase then decrease, the inflection point appeared when theratio of inoculation was around3%. Except of the cohesiveness, the texture properties first increase and then decrease with the increase of the ratio of milk powder and purple sweetpotato flour; the familiar trend of all the indictors was also found with the increase offermentation temperature, the inflection point appeared at about42℃. The contrast oftexture properties between purple sweet potato yogurt and ordinary yoghurt showed thatthe hardness and adhesiveness of purple sweet potato yogurt were significantly higher thanordinary yogurt, and no significant difference was found between other three parameters.4. The flavor components of purple sweet potato yoghurt and ordinary yoghurt wereanalyzed by headspace solid-phase micro-extraction coupled with gas chromatography--mass spectrometry. The kinds of flavor components detected in the two samples werenearly the same. Aldehydes, ketones, acids, esters, aromatic compounds, sulfurcompounds, terpenoid compounds, furan and alcohols were existed in both ordinaryyoghurt and purple sweet potato yoghurt. There were four mainly difference between theordinary yoghurt and the purple sweet potato yoghurt. Firstly, the quantity of thecompounds in the purple sweet potato yoghurt was more, the number of compoundsexisted in the purple sweet potato yoghurt was97while the ordinary yoghurt was43.Secondly, the acetaldehyde was only found in the purple sweet potato yoghurt. Thirdly, thequantity of the terpenoid compounds existed in the purple sweet potato yoghurt was more.Fourthly, the esters existed in the purple sweet potato yoghurt contains not only shortchain aliphatic esters and lactones but also esters of long–chain fatty acid, while theordinary yoghurt mainly contains short ones.5. The correlation analysis between the sensory evaluation parameters and theinstrumental measurement parameters was attempted. It showed that the shape durability,gliding property and spinnability have an extensive correlation with TPA parameters(r=0.694～0.988,P<0.05or P<0.01). And there was no significant correlation betweenTPA parameters and the consistency, as well as the oral retention.