Grain Processing (8)
Authors: Jiang Lihua, Ying Xin, Gu Jinghan, Zhang Yan, Pang Meirong
Keywords: food additives; bread; mechanism of action; applied effect
Abstract:The degree of research and development and application of food additives is one of the signs of the development level of a national food industry, and the rational use of food additives can not only maintain food safety, but also promote the rapid development of the food processing industry. In industrially processed bread products, food additives play a pivotal role, which can play a role in improving product color, flavor, texture, quality, maintaining nutritional value and extending shelf life. The mechanism of action and application effect of enzymes, emulsifiers, preservatives and antioxidants commonly used in bread are reviewed, in order to provide reference and guidance for the use of food additives in bread and avoid adverse effects due to the irrational use of food additives.
Food additives are widely used in bread, according to GB2760-2014 (food safety national standard food additive use standards) provisions, bread allowable additives include preservatives, antioxidants, leavening agents, stabilizers, emulsifiers, sweeteners, moisture retention agents, acidity regulator thickeners, colorants and enzyme preparations. In this paper, the mechanism of action and application effect of the more commonly used additives in bread are reviewed.
1 Types of additives commonly used in bread
The additives used in bread are classified and summarized, and it is found that the additives used in the current commercially available bread are mainly compound additives, which include enzyme emulsifiers, preservatives and antioxidants (remove the bread raw materials themselves such as fillings, grease and other additives with people).
2 Mechanism of action and application effect of the enzyme preparation
Enzyme preparations are one of the commonly used additives in bread, usually in the compound type, especially in long-term bread and whole grain bread. Enzymes commonly used in bread include amylase, lipase, xylanase and glucose oxidase.
2.1 Mechanism of action and application effect of amylase
Amylase is a relatively complex and large enzyme family, which can be divided into a-amylase, β-amylase, glucoamylase, prolanase and cyclodextrin glucose transferase according to different modes of action. The modes of action of the various enzymes are shown in Table 1.
Wheat itself contains a-amylase and β-amylase, which break down starch into soluble sugars and provide an energy source for yeast fermentation. However, during processing, the enzyme viability of wheat source will inevitably decrease, and the a-amylase contained in wheat itself is usually not enough to meet the production needs of baked products, so additional amylase is usually needed to help with starch hydrolysis. Figure 1 shows the hydrolysis of starch without amylase (left) and amylase (right) in sugar-free dough, it can be seen that in the case of no addition of amylase, starch is hydrolyzed by amylase in wheat into maltose into yeast cells, when yeast uses maltose, it takes about 2h to start fermentation induction period, so there will be a gap in the middle. After the addition of amylase, the starch can be hydrolyzed to glucose and then entered into human yeast cells, which greatly shortens the time for yeast to use glucose.
Amylase degrades starch into maltose, glucose dextrin and other products, thereby providing yeast with the energy needed for fermentation, shortening the fermentation time, increasing the volume of bread, and promoting the occurrence of the Maillard reaction.
Matsushita et al. added 0.025% a-amylase (1500U/g) to the mixture of whole wheat flour and white flour, and found that compared with the unaddressed group, the dough holding capacity was significantly enhanced, and the bread specific capacity was 5.08 cm3/g, an increase of 14.7%. Increasing amylase activity has a significant effect on bread volume, but excess a-amylase will hydrolyze a large amount of starch during the baking process, resulting in a weakening of the ability of starch to form a gel during the cooling process, which instead reduces the volume of bread. Xu Xiaojuan found that in the range of 20 to 80mg/kg, with the increase of amylase addition, the specific capacity of whole wheat bread gradually increased, reaching the maximum when the addition of amylase was 80mg/kg, and the amylase capacity began to gradually decrease.
In addition, amylase can keep the bread structure soft and reduce the starch recrystallization rate, slow down starch aging, and prolong shelf life. Li Jing et al. studied that maltose amylase from Bacillus subtilis can delay the decline of bread quality, and the addition of 0.04% maltoamylase can significantly delay the aging of bread, and the gelatinization characteristics of the starch of the opposite group have less effect. On the seventh day of storage, the bread can reduce the water loss by 36.92% and can maintain the elasticity of the bread.
2.2 Mechanism of action and application effect of lipase
Lipase can catalyze the decomposition, synthesis and transesterification of ester compounds, etc. Under normal conditions, lipase may simultaneously exhibit the activity of one or more of the enzymes such as triglyceride enzymes, phospholipase, and glycolipase. It can decompose triglycerides into mono/diglycerides when it is manifested as triglyceride activity; lecithin can be decomposed into hemolytic lecithin when it is manifested as phospholipase activity; the molecular structure is similar to that of monoglycerides of diacetylate tartarate, and when it is manifested as glycolipase activity, it can decompose bis galactose diglycerides into bis galactose monoglycerides, and the molecular structure is similar to sodium stearoyl lactate. It can be seen from the decomposition products of lipase that the role of lipase is similar to that of emulsifiers, in bread, the main role of lipase is: (1) increase the volume of bread: the hydrolysis of lipase can form a stronger polar and hydrophilic structure, better binding with wheat gluten, forming a stronger gluten network; (2) delaying the aging of bread: lipase decomposition produces esters / lipids have an emulsifier effect, triglyceride lipase hydrolysis of fat to form glycerol can combine with starch to form a complex, delaying starch aging.
Wang Jiabao et al. showed that the bread specific capacity of 0.01 g lipase/kg flour and 0.5 g of mono-diglycerides/kg of diacetylate tartaric acid was increased by 6.7% and 11.3% respectively compared with the control group, and the hardness values of the two groups of bread after storage for 15 days were significantly higher than those of the control group, but there was no significant difference between the two groups. However, there are also studies that show that lipase reduces the specific volume of bread, and Altinel et al. have shown that after adding 0.0002% lipase, the specific volume of bread decreased by 4.82% compared with the control group; when the amount of addition was increased to 0.001%, the specific volume of bread was not significantly different from that of the control. This phenomenon is caused by the destructive effect of free fatty acids and other lipid degradation products produced by the action of lipase in the dough.
2.3 Mechanism of action and application effect of xylanase
Xylanase refers to a group of enzymes that can specifically degrade hemicellulosic xylans into xylan oligosaccharides and xylose. Water-insoluble xylan is highly absorbent, competing with gluten protein to absorb water, making gluten protein insufficient water absorption, thereby weakening the gluten network. After the partial hydrolysis of water-insoluble xylan, xylanase contributes to the formation of gluten network, improves the strength and elongation of gluten-starch film, increases the ability to hold gas and water, makes bread softer, and delays bread aging.
Xylanase is usually used in whole wheat bread, compared with white flour, whole wheat flour has a high dietary fiber content, about 12%, its main component is arabinoganate, divided into water-soluble and water insoluble, of which water insoluble accounts for 70% to 75%, which causes a destructive effect on the gluten network of whole-wheat dough, from a microstructure point of view, there are many cracks and large holes in the structure of whole wheat dough, after adding 0.03% xylanase reaction for 90min, the gluten structure becomes more continuous, Holes are significantly reduced. Studies such as GHOSHAL have shown that xylanase can reduce the hardness value of whole wheat bread during storage, delay aging, and improve sensory scores. In the whole wheat bread added 30, 60, 90 mg / kg of xylanase, with the increase of the amount of addition, the hardness value of whole wheat bread gradually decreased, the elastic value gradually increased, compared with the control, after the addition of 90 mg / kg of xylanase, the elastic value increased by 16.2%, the hardness value decreased by 12.5%.
2.4 Mechanism of action and application effect of glucose oxidase
Glucose oxidase is an aerobic dehydrogenase with good oxidation and is considered "the most promising green wheat flour reinforcing agent". Glucose oxidase oxidizes glucose to glucose lactone and hydrogen peroxide, which has strong oxidation properties, oxidizes the pornyl group to disulfide bonds, strengthens the gluten structure, improves the processing characteristics and stability of flour, helps to delay bread aging, and enhance flexibility.
Deng Jialuo et al. studies have shown that after adding 15mg/kg glucose oxidase, the specific volume of bread increased by 27.5%, and after adding 20mg/kg glucose oxidase, the hardness, stickiness and chewability of bread were significantly different from those of the control group. In frozen dough, the addition of 0.015% glucose oxidase improves the specific volume, elasticity, resilience and sensory score of frozen dough baked bread, improving overall quality. In the whole wheat dough, human glucose oxidase 5Ug flour is added to catalyze the hydrogen peroxide produced by glucose oxidation, and the carotenoid content in the dough drops by 40%, which plays the role of bleaching whole wheat flour. At the same time, glucose oxidase increases the elastic modulus (G') and viscous modulus (G") of the dough, resulting in an increase in the hardness of the dough, so when adding glucose oxidase to the whole wheat dough, you should pay attention to adding doses to avoid the dough being too hard.
3 The mechanism of action and application effect of emulsifier
In bread, the emulsifier can play a soft and fresh effect, because the amylose becomes a spiral structure under heating conditions, and after adding a human emulsifier, it will complex with this spiral structure to form a complex, thereby increasing the gelatinization temperature of starch, preventing starch recrystallization, and preventing amylose condensation from inside the starch, thereby delaying the aging of bread.
Interactions between emulsifiers and proteins may also occur, in particular by binding to amino acids of non-polar hydrophobic groups, by virtue of hydrogen bonds to amino acids containing uncharged polar groups, or by electrostatic interaction with amino acids containing charged polar groups, through these interactions can strengthen the gluten structure and improve chewability.
Zhong Baoyu et al. have shown that the addition of polyglyceride fatty acid ester with mass fraction of 0.25% to 1.0%, glyceryl monolaurate of 0.1% to 0.7% and sodium stearoyl lactate of 0.05% to 0.20% respectively added to the bread, with the increase of emulsifier addition, the specific volume of bread gradually increased, and the hardness of the bread was lower than that of the control group during the storage period of 7d. The optimal combination was 0.75% polyglyceride fatty acid ester, 0.60% monolaurate, and 0.15% sodium stearoyl lactate, and the bread prepared with this formula had a specific capacity of 5.87 mLg and a hardness of 474.4 g, which was 20% higher and 22% harder than the control group.
In frozen dough, as the amount of sodium stearoyl lactate added increased, the hardness of baked bread in frozen dough decreased first and then increased, and the elasticity, recoverability, specific volume and sensory score increased first and then decreased, and when the amount of SSL added was 0.20% (in terms of flour), each index reached its own peak.
The largest application of monostearate glycerides in the food field is bread, studies have shown that the addition of 0.3% monoglyceride can reduce the hardness of bread during storage period; 0.2% monoglyceride can improve the stability of dough fermentation, enhance the shock resistance of dough, and monoglyceride can also reduce the bubbles generated on the surface of bread baking.
4 The mechanism of action and application effect of antioxidants
L-ascorbic acid, L-ascorbyl palmitate is an antioxidant commonly used in bread. L- ascorbic acid has a strong reducivity, the oxidation mechanism of the opposite group is more complex, it is under the catalytic action of a complex system, it is converted into an oxidizing dehydrogenation L- ascorbic acid, on the one hand, oxidation of glutathione in the dough, so that the protease loses activity, inhibits the hydrolysis of gluten protein, relatively enhances the strength of gluten, on the other hand, the oxidizes the thiol group to disulfide bonds, strengthens the main network structure of gluten protein. Li Lijie et al. show that after adding 0.002% L-ascorbic acid, the specific volume of bread increased by 50.6%, and when stored on day 5, the hardness, adhesion and chewability of bread decreased by 31.8%, 29.4% and 26.8%, respectively. However, Qi Linjuan et al. found that the effect of L-ascorbic acid varies according to wheat varieties, and the improvement effect on the baking quality of wheat flour bread with different tendon strengths is different.
L-ascorbyl palmitate is a hydrophilic L-ascorbic acid and hydrophobic palmitate formed by ester bond binding to form a biparonic compound, which not only retains all the physiological activities of ascorbic acid, but also improves the tolerance to light, humidity and temperature. The long fatty acid chain in L-ascorbyl palmitate is well embedded into the spiral cavity of amylose, forming a polymer matrix of L-ascorbyl palmitate combined with starch, thereby inhibiting starch crystallization and aging. Serfert et al. confirmed that the addition of 0.38% L-ascorbyl palmitate to bread can effectively shorten the waking time of dough, make the bread form a loose and porous texture, and improve fluffiness and softness.
5 The mechanism of action and application effect of preservatives
According to GB2760-2014 (National Standard for Food Safety And Use of Food Additives), preservatives allowed to be used in bread include ε - polylysine, streptococcus lactate, sorbic acid and its potassium salt, propionic acid and its sodium salt, calcium salt and dehydroacetic acid and sodium salt (also known as dehydroacetic acid and its sodium salt). The bacteriostatic mechanism and bacteriostatic capacity of the 5 preservatives are shown in Table 2.
Due to the different effects of different preservatives on microorganisms, when several compounds are used, the bacteriostatic effect can be complementary and play a synergistic role. Mason Liu et al. have shown that when sodium dehydroacetate is compounded with calcium propionate in a 2:3 ratio, the bacteriostatic effect is the best. Preservatives added to the bread also has an impact on the shelf life, bean Corning and others compared the calcium propionate mixed addition, wrapping addition and smearing three ways on the shelf life of bread, of which the epidermal wrapping refers to the first calcium propionate mixed with 10g of dough, and then rolled into a thin skin wrapped on the dough, epidermal coating refers to the calcium propionate mixed into a 10% solution, and then brushed on the dough. The results show that the epidermal application has the best anti-mildew effect on the bread, followed by the epidermis wrapping, and finally the mixing and adding.
6 Summary and Outlook
Food additives play an important supporting role in the development of the food industry and are a powerful tool to solve various food problems. The function of a single food additive has certain limitations, and the composite use of multiple additives achieves synergistic effect, so in practical applications, composite additives are commonly used, especially in bread products, and a single food additive is often not used.
According to GB 2760 -2014 (Food Safety National Standards for the Use of Food Additives) one of the provisions of the same function of food additives (the same color colorant, preservative antioxidants) in the mixed use, the sum of the proportion of each dosage to its maximum use should not exceed 1. And under the premise of achieving the desired effect, the amount of use in food is reduced as much as possible. Although compound food additives can give food better quality, it is easy to lead to the problem of excessive use of additives or duplicate types, which is not in line with the development trend of food cleanliness and health. Therefore, food practitioners should have a clear understanding of the function and role of food additives, merge additives with the same function as much as possible, and scientifically and reasonably compound and add, so as to play the best effect of food additives.