| Oat is one of the best nutritional value cereals. And it has attracted considerable interest for its high fermentability with lactic acid bacteria in product development. The properties of oat sourdough fermented with Lactobacillus plantarum and its application in bread were studied in this paper. The acidification and aerobic plate count of the dough were analyzed to indicate the growth of lactobacillus. We also put emphasis on the changes of pasting properties of sourdough, protein solubility, in vitro digestibility and amino acid composition during fermentation. Response surface methodology (RSM) were used to optimize the process condition of oat sourdough when applied in bread. Four different kinds of breads were analyzed for their baking properties, storage properties and flavor compounds in order to explore the effects of oat sourdough starter on bread.Lactobacillus plantarum growed rapidly in oat medium with high capacity of acid production. During fermentation, organic acids were accumulated. Reduced sugar content first rised then declined. The pasting properties of the oat sourdough were determined with a Rapid-Visco Analyser (RVA). The results showed that peak viscosity, trough and final viscosity all decreased during fermentation. The protein wrapped in the outer layer of starch molecules was dissolved. Thus, the anti-cutting ability was weakened and breakdown values increased. The setback values, an indication of the tendency to retrograde upon cooling, decreased with increased fermentation periods. This observation suggested that the tendency to retrograde reduced as the fermentation time increased.Fermentation resulted in significantly (p<0.05) increase in protein solubility. After fermentated for 24 h and 48 h, the protein solubility increased by 19.50% and 54.06%, compared to the control without fermentation. In vitro digestibility of protein was assessed based on pepsin-trypsin two-step digestion. After fermentation, the protein digestibility was significantly increased (p<0.05). The amount and composition of total amino acids in oat protein didn't change very much. But the amino acid scores (AAS) increased from 71.53 to 76.60 after fermentation 48 h and the protein efficiency ratio (PER) had also enhanced.Two factors, fermentation time and amount of oat sourdough were assigned with a central composite face-centered design using Design Expert software to study the effect of sourdough on bread baking properties, using specific volume, crumb firmness and sensory evaluation as response values. We obtained the optimized condition of oat sourdough was: 14.5 h of fermentation time, 10% of amount.Common wheat bread, common oat bread (20% (w/w) oat flour substitution), oat sourdough bread (10% oat flour substitution+10% oat sourdough substitution) and freeze-dried oat sourdough bread (10% oat flour substitution+10% freeze-dried oat sourdough substitution) were analyzed to explore the effect of sourdough on bread properties. The results showed that sourdough improved the gas retention capacity and increased the bread specific volume. TPA parameters showed that the quality of oat sourdough bread was better than common oat bread. Sensory evaluation also showed oat sourdough bread was accepted by consumers. From the TPA parameters, water migration and aging enthalpy, we saw that sourdough can delay the deterioration of bread quality, the firming rate and aging enthalpy reduced during storage.These four kinds of breads were analyzed for their volatile compound composition by solid phase micro-extraction/gas chromatography-mass spectrometry (SPME/GC-MS) in order to explore the effects of oat sourdough starter and freeze drying of sourdough on volatile flavor compounds of bread. The compounds identified in the four breads were alcohols, acids, aldehydes, esters, ketones, aliphatic compounds, aromatic and heterocyclic compounds. The most abundant volatile compound category in all samples was alcohols, followed by aromatic and heterocyclic compounds, aldehydes and acids. Breads supplemented with oat flour had more kinds of volatile compounds. Toluene, heptanol, trimethylene acetate, caprylic acid were determined in oat breads but not in wheat bread. Some flavor compounds or flavor precursors were lost during freeze drying. Comparing with the other samples, oat sourdough bread owned some unique flavor compounds. |
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