I. Definition and principle
Definition: A method of food processing. The processed food is placed in a closed container, and the pressure is suddenly decompressed after heating and pressing, and the moisture in the food is vaporized and expanded, so that many small holes appear in the food, and become crispy, and become a puffed food. It is characterized by high temperature (130-180 Â° C) and short time (15-30 s).
Principle: When the grain is placed in the extruder, as the heating and pressurization progress, the water in the grain is overheated and the grain itself becomes soft. When a certain high pressure is reached and the expander cap is opened, the high pressure quickly becomes normal pressure. At this time, the water in the superheated state of the grain suddenly explodes and instantly explodes, and the water molecules can expand about 2000 times. The huge expansion pressure not only destroys the external morphology of the grain, but also breaks the molecular structure inherent in the grain, and cuts the insoluble long-chain starch into water-soluble short-chain starch, dextrin and sugar.
As a result, the insoluble matter in the puffed food is reduced, and the water-soluble substance is increased.
According to the number of screws, it can be divided into: single-screw extruder (by pushing the material and the friction of the wall), twin-screw extruder (two screws placed side by side).
According to the processing steps, it can be divided into: dry extruder (one-step expansion), mixed extruder (two-step expansion, raw material pre-heating, pre-cooking treatment)
Third, the factors affecting the effect of puffing
Raw materials: type, moisture, physical state, chemical composition (starch, protein, fat, amount and type of sugar), pH.
Extruder type and physical parameters: screw number, geometry and speed, cylinder inner diameter and length, compression ratio, spiral angle.
Puffing process: time, pressure, temperature, die diameter, shear force.
Fourth, the advantages and disadvantages of puffing treatment on feed and principles
Lee: Proper expansion can reduce the anti-nutritional factors and improve the digestion and utilization of feed protein, oil, carbohydrates and fiber.
Disadvantages: Excessive expansion leads to loss of nutrients (amino acids, vitamins, etc.).
Principle: Maintain a balance between reducing anti-nutritional factors, increasing nutrient digestibility, and reducing nutrient loss.
V. Changes in the physical and chemical properties of raw nutrients during the expansion process
Moderate puffing can destroy the spatial folding structure of the protein, improve the digestibility, inactivate the anti-nutritional factors (trypsin inhibitor, hemagglutinin, tannin, phytic acid, etc.), high temperature, high proportion of protein materials, high screw speed during expansion. Can increase the protein digestibility of materials. Excessive expansion will cause the Maillard reaction to occur.
2, amino acid
Partial loss, participation in Maillard reaction or formation of acrylamide. High screw speed and high feed rate during expansion can increase the lysine retention rate of the material, and the high ring mold diameter and high moisture can reduce the lysine retention rate of the material.
Maillard reaction: carbonyl compound (reducing saccharide) + amino compound (amino acid and protein) â†’ brown (black) black essence (imitation melanin).
Participation in the reaction of reducing sugar: five carbon sugar browning speed >> six carbon sugar (about 10 times), and ribose > arabinose > xylose, galactose > mannose > glucose.
Participates in the reaction of amino acids: lysine, arginine, tryptophan, cysteine, histidine, and lysine has the highest reactivity.
Temperature: 20 to 25 Â° C can react. Generally, each phase has a difference of 10 Â° C, and the reaction speed differs by 3 to 5 times. The speed is higher than 30 Â° C. When the temperature is higher than 80 Â° C, the reaction speed is less affected by temperature and oxygen.
Moisture: When it is 10% to 15%, the reaction is easy to occur, and a completely dry food is difficult to occur.
When the pH is 3 or more, the reaction accelerates as the pH increases.
Acrylamide: A carcinogen that is found in foods such as potatoes, biscuits, and bread made at temperatures above 120 Â°C.
Participation in the reaction of amino acids: asparagine>>cysteine, glutamine, arginine, and aspartic acid.
Participate in the reaction of reducing sugar: glucose, oligosaccharides.
Inhibition of reactive amino acids: glycine, lysine.
3, carbohydrates - starch gelatinization, digestibility increased; non-digestible fiber into soluble fiber or simple sugar
Monosaccharide: Partial loss, monosaccharide can undergo multiple reactions with other substances during the expansion process, so it is necessary to control the level of free monosaccharide in the puffed raw material.
Harmful oligosaccharides: The levels of raffinose and stachyose are significantly reduced.
Starch: gelatinization, amylopectin is more easily degraded, and amylose can form an amylose-fat complex with monoglycerides and free fatty acids in the diet.
Fiber: Light and moderate puffing conditions have no effect on the raw fiber, but puffing under high conditions can increase the soluble fiber level of the raw material.
4, fat - rancid rate decreased, shelf life is extended; fat cells rupture, oil digestibility increased
Hydrolase inactivation: lipase, lipoxygenase, peroxidase.
Natural antioxidant release: Vitamin E and its analogues.
Complex with carbohydrates: The ratio of binding is 1 to 10 (the total fat content is determined by acid hydrolysis instead of the usual ether extraction method).
Higher storage and transportation requirements: cell rupture, free fatty acid exposure.
5, vitamin - loss rate of 15-100%, can use high temperature resistant raw materials or puffed to supplement
Fat-soluble vitamins: Vitamin D and K are better than A and E for heat and oxygen (expansion).
Vitamin B1: high temperature, high screw speed, high pH can reduce the retention rate of material B1, high moisture, high feed rate can increase the retention rate of material B1.
Vitamin B2: High temperature and high moisture have no effect on B2 stability, and high screw speed reduces material B2 retention.
6. Minerals - Increase the utilization of plant phosphorus, but no benefit to other mineral elements.
7, moisture - reduce
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