| Tofu,as a traditional soybean product in China,is rich in protein,fat,carbohydrates and a variety of trace elements,and is deeply loved by consumers.However,tofu products have a short shelf life and can not be sold for a long time,which greatly hinders the rapid development of tofu industry.In this paper,a kind of firm Tofu was used as the research subject and during storage,the best coating substrate according to the change of the quality of tofu was selected.The relationship between the fresh-keeping effect and the film properties was further explored.Then microcapsules containing clove essential oil and cinnamon essential oil were prepared and characterized to verify the formation of microcapsule products.The microencapsulated products were added to the composite coating to study the effect of those antibacterial treatment on the shelf life and quality characteristics of tofu at different storage temperatures,and the most suitable microencapsulated antibacterial coating for tofu preservation was established.The main results are as follows:Chitosan-soybean protein isolate composite film is better than single chitosan and soybean protein isolate coating,and 2.0%CS+0.5%SPI coating has the best effect,which could prolong the shelf life of tofu at 20 ℃ to 32 hours and effectively restrained the change of p H value and the decrease of sensory score of tofu.The fresh-keeping effect of the composite film was further verified,and the results showed that the composite coating could more effectively inhibit the deterioration of tofu color and texture index.The relationship between the freshkeeping effect of the composite coating and the film was studied.The results showed that the film formed by adding a small amount of soy protein isolate into chitosan had higher mechanical strength and better barrier property.The coating on the surface of bean curd surface was denser,less void,more uniform and had a continuous thickness.Clove essential oil and cinnamon essential oil microcapsules were prepared by saturated solution method.the microencapsulated products were white powder with light fragrance,uniform particle size and good regularity of microcapsule particles.The components of essential oils before and after embedding were analyzed by GC-MS,and it was found that the main antibacterial components of the two kinds of essential oils were improved to a certain extent.The two kinds of microcapsules were characterized by thermogravimetry,infrared spectroscopy,ultraviolet spectroscopy and scanning electron microscope,and the formation of microcapsules was verified.The essential oil microcapsule was added to the composite coating solution to prepare the microcapsule antibacterial coating film.The quality of tofu treated with different antibacterial coating was studied at 35 ℃,20 ℃ and 4 ℃ at different storage temperatures.The fresh-keeping effect of microcapsules was positively correlated with the addition of microcapsules,and the preservation was more effective with cinnamon essential oil microcapsules compared with clove essential oil microcapsules.The best effect on Tofu preservation was found with 1.0% cinnamon essential oil microcapsule antibacterial coating treatment,which could prolong the shelf life of tofu to about 10 h,72 h and 20 d at 35 ℃,20 ℃and 4 ℃,respectively.Compared with other treatments,1.0% cinnamon essential oil microcapsule antibacterial coating could significantly inhibit the accumulation of total acid content,TVB-N value and peroxide value of tofu at different temperatures,improve the safety of tofu products,and effectively inhibit the decrease of sensory score and the deterioration of apparent state of tofu.The microstructure of the coating formed by microcapsule antibacterial coating was analyzed,and the results of scanning electron microscope showed that the microcapsule formed by clove oil was agglomerated in the coatings;on the other hand,cinnamomum essential oil microcapsule was more uniform and the particles formed by the microcapsules could be better distributed in the coatings. |
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