| Laver（Porphyra spp.）is one of the most commercially available marine crops in coastal areas of China,which is widely welcomed among consumers due to delicious taste and rich nutritional value.However,a large portion of products are mainly dried,and the product types are single.High moisture instant seasoning algae food has good market prospect,which satisfy consumers’demand for nutrition,health and convenience.Thermal sterilization is the main technical means to achieve high moisture instant algae food preservation at room temperature.However,the color and texture as two main indicators are used to evaluate the quality of instant laver products.Because of the extreme thin leaves and soft texture,laver is prone to change in color and texture during thermal sterilization process,which might seriously affect its edibility and commercial value.The influence of thermal processing and acidification on quality of high-moisture laver is still unclear.No effective method has been proposed for improving the quality of high-moisture laver after sterilization.Therefore,this paper took laver as the research object,clarified the effects of heat treatment and acidification on the characteristics of high-moisture laver from the aspects of sensory quality,physical,chemical index,and microstructure.On this basis,the sterilization process of acidic and low acidic instant laver products was optimized based on sensory and nutritional components.Finally,the texture quality of laver products after high pressure heat sterilization was improved by regulating water content and adding exogenous substances,and high-quality instant laver products was developed.The present research provided theoretical guidance for the development and quality control of high-moisture ready-to-eat laver products.In order to explore the quality change characteristics of laver during heat treatment,effects of two thermal treatments（sterilization at 118℃and pasteurization at 90℃）and acidification on color,texture,chemical composition,and microstructure of high-moisture laver were investigated.Results showed that the reddish-brown of laver faded to varying degrees after heating due to rapid degradation of phycoerythrin.With increasing heating time,the a*value gradually decreased accompanied by the increase in b*value,and the color changed to yellow-green.Besides,hardness and toughness gradually decreased,while adhesiveness increased.At the same heat treatment,the texture of laver treated by acidification was worse than that of the control group.Microstructure and soluble sugar results indicated that the cell tissue of the laver was destroyed after intensive heating.Intensive thermal processing accelerated quality deterioration as evidenced by pigment degradation,cell rupture,and increase in soluble substances.In order to reduce the deterioration effect of heat treatment on the quality of laver,the sterilization process of instant laver was optimized.The heat penetration curves during high pressure heat treatment（110℃,115℃,121℃）and normal pressure heat treatment（85℃,90℃,95℃）were measured for low acid laver and acidified laver（p H≤4.2）.The safe F value of sterilization corresponding to two sterilization methods was obtained by preservation experiments and microbial analysis.The effects of different temperature-time combinations with the same F value on the sensory and nutritional quality of laver were further explored.Results showed that low-acid laver could reach commercial sterility when F0=3 min under high pressure heat sterilization,and acidified laver could also reach the preservation requirements when938.8.39=5 min under normal pressure heat sterilization.The toughness,hardness and sensory score of laver increased with the increase of sterilization temperature under the same F value.In terms of nutrients,the soluble sugar,polyphenol,and total free amino acids decreased with the increase of temperature in the high-pressure group.The highest nutrition was obtained at 90℃in the normal-pressure group.In general,the texture,sensory and nutritional quality were better when the sterilization parameters are 90℃,11.5 min（acidified group）and 115℃,8 min（low acid group）.Compared with high-pressure heat sterilization,acidification combined with normal pressure sterilization exhibited better texture and color.In order to further improve the texture quality of laver after high-pressure heat sterilization,this paper continued to explore the effects of calcium salts,phosphates,and different water contents on the quality of laver.Taking sensory evaluation as the main standard,the optimum ratio was determined by single factor and orthogonal experiment.The results showed that different water contents had significant effects on the sensory of laver,and 80%～85%water content had the best sensory quality.The effect of phosphate on the texture improvement of laver was better than that of calcium salt.Single factor experiments showed that 0.4%disodium hydrogen phosphate,0.5%sodium pyrophosphate and 0.5%sodium tripolyphosphate respect-tively had higher texture quality.The influence order within the experimental concentration range is sodium pyrophosphate>sodium tripolyphosphate>disodium hydrogen phosphate.The best combination was 0.2%disodium hydrogen phosphate+0.3%sodium pyrophosphate+0.5%sodium tripolyphosphate.Compared with the group without phosphate addition,laver was more closely bound to water,with water holding capacity increased by 4.27%and soluble sugar decreased by 22.42%.Finally,different seasoning formulas and process parameters were proposed for two kinds of instant soft-packed laver products with low acidity and acidity.Two instant laver products with different tastes were developed,and the safety and sensory quality of the products during storage were further analyzed.The results showed that the microbial indexes such as E.coli and total bacterial count of the product were always within the safe range.The sensory quality showed a downward trend with the increase of storage time,but it still had good acceptance within 30 days of accelerated test at 37℃. |
