Study On Processing Technology And Quality Of Colored Tofu

Tofu is a traditional food in China,mainly made from soybeans.Although some studies about walnut tofu,peanut tofu and so on have been reported.At present,most of tofu sold in the market are single soybean tofu,which cannot meet consumers' requirements for the color,flavor,taste and product variety of food.This study intends to add some colored vegetables or fruits in the process of tofu production to produce new colored tofu,so that the produced tofu not only has an attractive color,but also has the aroma of beans and the clear fragrance of fruits and vegetables,laying a certain theoretical foundation for expanding the tofu market;the extension of its shelf life is also studied to improve the shortcomings of traditional bulk tofu that is not resistant to storage.The main research contents are as follows:(1)Using purple cabbage and soybean milk,cucumber and soybean milk,watermelon juice and soybean milk as raw materials,respectively,the response surface design was performed to optimize the production process of purple tofu,green tofu and red tofu.(2)The nutritional composition,texture and color of several kinds of tofu were compared;the flavor of several tofu samples were determined using electronic nose and SEMP-GC-MS(solid phase microextraction and gas chromatography-mass spectrometry)simultaneously.(3)The ?-polylysine,nisin,potassium sorbate were used as preservatives,and a mixture design was used to optimize the ratio of several preservatives using sensory scores and total number of colonies as response values.Tofu was treated with different sterilization methods,and then,the shelf life of tofu was investigated by using the comprehensive preservation technologies mentioned aboved.The results were as follows:(1)When the addition amount of purple cabbage was 25.0%,the addition amount of GDL was 0.18%,and the solidification temperature was 87?,the purple tofu obtained the best sensory score.The sensory score of green tofu was the highest under the optimized conditions of adding 33.0% cucumber,adding 0.18% GDL and setting temperature of 82?.Also,the quality of watermelon tofu was the best under the condition that the added amount of watermelon was 24.5%,the added amount of GDL was 0.22% and the solidification temperature was 85?.(2)The moisture content were 79.98%,75.23% and 76.99%,the protein content were 7.70%,6.88% and 7.74%,and the fat content(dry basis)were 29.95%,9.32% and 29.49% in purple,green and red tofu,respectively.The obtained tofu contained 8 kinds of essential amino acids needed for human,accounting for 46.30%,49.60% and 25.40% of all amino acids in three tofu respectively.A total of 85 volatile flavor compounds were identified and there were 46,54,and 64 kinds in purple tofu,green tofu,and red tofu respectively.Among them,purple tofu contained allyl isothiocyanate,a characteristic flavor of purple cabbage,green tofu contained the characteristic flavor substances(E,E)-2,4-Decadienal of cucumber;red tofu contained the characteristic flavor substance cis-3-Nonen-1-ol of watermelon.The electronic nose measurement showed that the whole flavor of green and red tofu was more similar.The hardness of tofu were negatively correlated with the moisture content,all of the three kinds of colored tofu had higher hardness,resilience,elasticity and chewability than common soybean tofu.The L* values,a values,and b values among the three kinds of tofu had significant difference.(3)The optimal formula of the preservation solution was determined using Design Expert 8.0 software,Including 0.30% of ?-polylysine,0.26% of nisin,0.30% of potassium sorbate,and 99.14% of water,respectively.Two kinds of sterilization methods were compared,and it was found that it worked best when tofu was pasteurized at 68? for 30 min followed by rapid cooling.Overall,when the tofu was first soaked into the above-mentioned preservation solution,and then sterilized at 68? for 30 minutes followed by quickly cooling and stored at 0-4?,the growth of microorganisms in tofu would be obviously inhibited and shelf life of colored tofu would be up to 16 d.