Study On The Production Process Of Extrusion Food Using The Blueberry Pomace

Blueberry fruits contain rich nutrients. It is recommended as one of the five kinds of healthy fruit by FAO. Blueberry pomace is the by-products of blueberry juice processing, but it still contains many essential nutrients and active ingredients, such as anthocyanins, flavonol, etc, with antioxidant, anti-cancer, enhancing immune function, and many other beneficients. In recent years, blueberry juice processing industry developing rapidly in our country. The traditional way of regarding pomace as waste produces resource waste and also causes environmental pollution. Therefore, using blueberry pomace to develop a new product or application way, will make great sense of blueberry production processing industry and environmental protection. This study use blueberry pomace as raw material, using twin-screw extruder for extrusion, inventing a blueberry flavor snack food. In addition, we analysised the ingredient of blueberry pomace and blueberry puffed food, optimized the ratio of raw materials and extruding process of expanded product. Main results are as follows:(1) The composition of the blueberry fruits and blueberry pomace is detected by using correlation methods of national standards, and the results are compared. The moisture content of the blueberry pomace is 57.62%, less than the data of the bluberry fruits’which reach to 80.43%. In addition, there is a small amount of protein, fat and so on. Meanwhile, the constants (K, Na) and trace elements (Ca, Mg, Fe, Cu), especially Fe, Ca in the blueberry pomace are detected by using the method of ICP-AES. The content of anthocyanin and flavonol reach to 2.551mg/g and 1.677mg/g by spectrophotometry, both of them are higher than the content in the blueberry fruits.(2) The raw material of the product is confirmed on the basis of preliminary experiments. Taking the sensory evaluation and radial expansion degree as the main standard, we designed the single factor experiment and orthogonal design experiment, to optimize the ratio of raw materials and additives. Single factor experiment found that blueberry quality than corn, xylitol content, oil content ever too high or too low will lead to a lower scores of the product of sensory evaluation and smaller radial expansion degree. If single factor is moderate, the sensory evaluation score will be higher, puffing effect will be ideal. The product optimal combination formula which determined by the orthogonal experiment is:blueberry powder 18%(corn 82%), xylitol 8%, oil content 2%. Poor and variance analysis results indicate that the order of the factors which influence the product quality is:xylitol> blueberries than corn> oil content, order of the factors that affect product puffing degree is:oil> blueberries than corn> xylitol. Among them, the xylitol content has a significant influence on product sensory index, blueberries corn ratio and oil content have significant influence on product radial puffing degree.(3) Take product moisture content, the product of radial puffing degree and rupture force as response values to carry on the three factors, four levels response surface experiment design on the basis of single factor experiment. We explored the impact of the raw material moisture content, the main screw speed, feed rate and heating temperature on the quality of the product. The best operating parameters are analysised to be raw material moisture content 11%, the screw rotation speed 190rpm, feeding speed 32rpm, four period of heating temperature 70℃-90℃-120℃-140℃ by the Design-export8.0 software, we will get lowest product moisture content as 6.4%, the smallest bursting strength value as 41.83 N, the biggest radial expansion degree as 3.9 in this condition.(4) Through determination of basic ingredients we found that moisture content is about 7.44% in blueberry puffed products.Mineral element content accounts for about 0.3% of the total, basically reached the same level of the blueberry pomace and exceed that of blueberry fruit, which contains K, Na, Ca, Fe, Mg, Cu, and other major and trace metal elements. Meawhile, puffed products is determined by spectrophotometric method, the content of anthocyanin and flavonols are found to be reduced, and at last the anthocyanin content is 0.025 mg/g, flavonol content is 0.725 mg/g in the product. Analyzed the blueberry products and properties of four kinds of commercial puffed food, we found that blueberry expanded product bulk density is 0.18 g/mL, less than four commercial puffed food, means the puffing effect is better. The rupture strength of the product is 41. IN, hardness is 48.8N measured by physical properties analyzer, which are better than commercial puffed food, means that the product is more crispy and less hard.The water soluble index and water imbibition index of the blueberry expanded product is 48.73% and 324.83%, which are similar to the extrusion products’which sold in the market, water soluble index is higher, water absorption index is lower relative to the baking and frying expanded food.