| Potatoes(Solanum tuberosum L.),also known as potatoes and potatoes,are annual herb belonging to Solanaceae.Their tubers are edible and they are a kind of crop with comprehensive nutritional components.Some of their nutritional components are much higher than other traditional staple foods,and potatoes are a kind of crop with both food and vegetable functions.In 2015,the Ministry of Agriculture proposed a strategy for potato staple foodization,proposing“actively promoting the development of potato staple food”.Potato snowflake powder is an important product of potato industry,high-quality potato snowflake powder can retain the taste and flavor of potatoes to the maximum extent after rehydration,but the potato snowflake powder prepared by traditional technology has poor rehydration,limiting its application in instant potato staple food products.With the deepening of potato staple food strategy and the acceleration of people’s life rhythm,the development of instant potato products has been a hot topic in the food industry.Vacuum freeze-drying process can effectively improve the poor rehydration of potato snowflake powder,which can keep the original properties of dried food raw materials after rehydration,and is widely used in the development of instant products.In this paper,potato snowflake powder was prepared by optimizing vacuum freeze-drying process using potato as raw material,and compared with hot-air drying process,and the advantages of vacuum freeze-drying process for preparing potato snowflake powder were determined by scanning electron microscopy,X-ray diffraction and thermal characteristics analysis.The optimum formula of vacuum freeze-dried instant mashed potato was determined by single factor and response surface optimization experiments.Finally,the optimum properties of instant mashed potato were determined by texture analysis,chroma analysis and rehydration analysis.The conclusions are as follows:1.Based on the freeze-drying rate,the freeze-drying process parameters of potato snowflake powder were determined.The results showed that the optimum freeze-drying conditions for vacuum freeze-dried potato snowflake powder were:sublimation drying vacuum100 Pa,sublimation drying temperature 76°C,analytical drying vacuum 70 Pa,analytical drying temperature 45°C and charge amount 7.5 kg/m~2.The verification test was carried out according to the above test conditions,and the freeze-drying rate was 11.262%/h.2.Observed by scanning electron microscope,the vacuum freeze-dried potato snowflake powder particles were more uniform and the surface wrinkles were smaller;X-ray diffraction results showed that vacuum freeze-dried potato snowflake powder could retain higher crystallinity and reduce structural damage;The results of thermal properties showed that vacuum freeze-dried potato snowflake powder had higher enthalpy value and better thermal stability during gelatinization,and its gelatinization degree was lower than that of hot air-dried potato snowflake powder.3.Based on the sensory score,the optimal formula of vacuum freeze-dried instant mashed potato was determined:based on potato snowflake powder,salt addition amount was 1.5%,monosodium glutamate addition amount was 1.0%,pepper addition amount was 0.3%,coriander addition amount was 6.0%and onion oil addition amount was 6.0%,at this time,sensory score was the best.The order of influence of each factor on the sensory score was:salt addition amount>monosodium glutamate addition amount>pepper powder addition amount>onion oil addition amount>coriander addition amount.4.The optimum rehydration ratio of instant mashed potatoes was determined to be 1:5 by texture analyzer;Colorimetric analysis showed that the color of mashed potato prepared by vacuum freeze-drying process changed slightly,and its quality was better than that of potato powder prepared by hot air drying;The rehydration of potato snowflake powder prepared by vacuum freeze-drying was better than that by hot air drying.5.According to the requirements of quality standards,the vacuum freeze-dried instant mashed potato prepared in this experiment was light yellow uniform snowflake or powder before rehydration;And it was yellowish brown with suitable salinity,rich potato aroma and uniform texture after rehydration.Before rehydration,the water content was 7.81%,ash content was 0.47%,reducing sugar content was 0.187%,arsenic content was 0.1 mg/kg and lead content was 0.1 mg/kg.The total number of colonies was 2 cfu/g,and no pathogenic bacteria such as Escherichia coli were detected. |
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