Bread processing and bread additives

Author: Xue Xiaoxian / Edited by Bai Diansheng
Publisher:
Publish Date: 2000-11-01
Features: This book consists of two parts. The first part introduces bread processing technology and basic knowledge; the second part covers the properties, functions, processing methods, and variety of bread additives. The book is easy to understand, combining theoretical knowledge with practical operational skills. It is suitable for individuals, collective enterprises, townships, state-owned enterprises, home workshops, as well as for training workers in the bread processing industry and for home learning. Excerpt: Swelling occurs when, upon heating, water molecules enter the starch granules, causing them to expand continuously. The volume can increase several to dozens of times before they rupture, a process called gelatinization. The swelling of starch granules to gelatinization occurs in several stages, each exhibiting different properties. The temperature at which starch gelatinizes is called the gelatinization temperature. For wheat flour, the gelatinization temperature ranges from 59.5 to 64°C. Therefore, the gelatinization temperature of starch is a major issue in bread production. If the temperature is too high during dough preparation, the starch granules may gelatinize prematurely, causing the dough to become sticky and affecting the final product's leavening. Starch granules are aggregates of many glucose molecules. The structure of the aggregates is radially dispersed around a central point. The intermolecular attraction between these aggregates is very strong. Water molecules find it difficult to enter the aggregates, so starch is insoluble in cold water. During the baking process of the dough, as the temperature rises, the kinetic energy of the aggregate molecules increases. When this energy exceeds the intermolecular attraction, the aggregates break. The broken aggregate molecules then spread in all directions, allowing a large amount of water to enter the aggregates. The expanded aggregate molecules link together to form a hydrated gel network, which is gelatinization, also known as α-hydrolysis. Gelatinized starch, due to its increased surface area, is more easily hydrolyzed by enzymes in the human digestive system, thereby improving digestibility. After gelatinization, as the number of starch gelatinized particles increases, the viscosity of the starch paste also increases. When gelatinized starch cools, the expanded and disordered aggregate molecules contract and cluster together, causing starch products to become firmer. If a starch solution becomes cloudy, the solubility of the solution decreases, the solute precipitates, and the precipitate is insoluble and not easily hydrolyzed by enzymes. This phenomenon is called starch retrogradation or coagulation. Starch retrogradation is of great significance in bread production, directly affecting the quality and digestibility of bread. Measures to prevent retrogradation:
1. Consider the starch structure composition. Linear starch molecules have fewer spatial barriers and are prone to aggregation and association, making them more susceptible to retrogradation. Branching starch molecules have a branched structure with significant spatial barriers, making them less prone to aggregation and association, and thus less susceptible to retrogradation. Among linear starch molecules, those with moderate chain lengths are more prone to retrogradation. Chains that are too long create spatial barriers, while those that are too short are easily dispersed, so neither is prone to retrogradation.
2. Temperature conditions. The optimal temperature for starch retrogradation is 2–4°C. Retrogradation does not occur at temperatures above 60°C or below ?20°C. Slow cooling allows time for starch molecules to orient and arrange, accelerating retrogradation; rapid cooling prevents molecules from orienting, thus reducing retrogradation. Refrigerated bread, instant cooked rice, or instant noodles take advantage of this principle.
3. Moisture content. When the moisture content in food is between 30% and 60%, starch is prone to retrogradation. Controlling the moisture content below 10% (in a dry state) or above 60% makes retrogradation less likely.
4. Control of pH. Starch retrogradation is slower at appropriate pH levels. Starch retrogradation is slow under acidic conditions (pH < 4) or alkaline conditions (pH > 8).
5. Addition of surfactants. Adding phospholipids, glycosides, soy protein, or other emulsifiers to starch can delay retrogradation. This is because they can reduce surface tension, produce emulsification, form a film between starch aggregates, and prevent hydrogen bonding mediated by water molecules, thereby delaying retrogradation.