Enhancing the freezing–thawing tolerance of frozen dough using ε-poly-L-lysine treated yeast

Metabolomic insights into the effect of chickpea protein hydrolysate on the freeze-thaw tolerance of industrial yeasts

The use of frozen dough is an intensive food-processing practice that contributes to the development of chain operations in the bakery industry. However, the fermentation activity of yeasts in frozen dough can be severely damaged by freeze-thaw stress, thereby degrading the final bread quality. In this study, chickpea protein hydrolysate significantly improved the quality of steamed bread made from frozen dough while enhancing the yeast survival rate and maintaining yeast cell structural integrity under freeze-thaw stress. The mechanism underlying this protective role of chickpea protein hydrolysate was further investigated by untargeted metabolomics analysis, which suggested that chickpea protein hydrolysate altered the intracellular metabolites associated with central carbon metabolism, amino acid synthesis, and lipid metabolism to improve yeast cell freeze-thaw tolerance. Therefore, chickpea protein hydrolysate is a promising natural antifreeze component for yeast cryopreservation in the frozen dough industry.

Microbiota structure of traditional starters from around the Tai-hang mountains and their influence on the fermentation properties, aroma profile and quality of Chinese steamed bread

BACKGROUND

Steamed bread is a popular staple food in China, and the significant regional differences of the microbiota in traditional starters make the flavor and quality of steamed bread highly variable along with long preparation times. Therefore, analyzing the microbial flora of traditional starters and their influences on the flavor and quality may help to solve the problems mentioned earlier, and it may also be conducive to potentially meet consumer needs and permit industrialization of this traditional fermented food.

RESULTS

One hundred and thirty-two fungal and 50 bacterial species were identified in five traditional starters, each with a different dominant genus. The fermentation properties of dough showed that total titratable acid, dough volume and gas production increased and the pH decreased with fermentation time. The traditional starters improved the quality of Chinese steamed bread (CSB) including the crumb structure, specific volume and sensory attributes. Thirty-three aroma compounds with a VIP (variable importance for the projection) > 1 were identified as characteristic aroma compounds. The correlations among the microbiota, aroma and qualities of CSB showed a greater contribution from the bacteria, which was consistent with the predictions of metabolic pathways in the sequenced genomes.

CONCLUSION

The quality of CSB fermented with traditional starters was improved induced by their different microbial profiles, and bacteria made a greater contribution than fungus to the aroma and qualities of CSB. © 2023 Society of Chemical Industry.

New insights into the alleviating role of starch derivatives on dough quality deterioration caused by freeze

The alleviating role of starch derivatives on the quality deterioration of frozen steamed bread dough was investigated in terms of derivative structure, the bread characteristics and dough properties including freezable water contents, yeast activity as well as dough viscoelasticity. The addition of starch derivatives including short-clustered maltodextrin (SCMD), DE2 maltodextrin (MD) and pregelatinized starch (PGS) significantly increased the specific volume and decreased the hardness of steamed bread compared with Control bread after 8-week frozen storage. Lower freezable water content was found in PGS dough than SCMD dough, which was consistent with the results of water absorption index of starch derivatives. The analysis of dough gassing rate and yeast survival ratio demonstrated SCMD could provide more cryoprotection for yeast cells. Meanwhile, a higher elastic module and a more continuous gluten-network structure of SCMD dough were found after 8-week frozen storage. These results indicated starch derivatives especially SCMD were promising to be used as the alternative improvers in frozen dough production.

Thermal-aggregation behavior of gluten in frozen dough induced by ε-poly-L-lysine treated yeast

ε-poly-L-lysine treated yeast (PTY) helps to enhance the freeze-thaw tolerance of frozen dough. This study explored the effect of PTY on the aggregation and the gas-retention of frozen dough after steaming for 2, 5, 10, and 20 min. Gas-cell images showed that PTY reduced the loss of gas-retention ability caused by 4 times of freeze-thaw. The results of sodium dodecyl sulfate extractability and subunit distribution of gluten showed that, after the same heat time, frozen dough with PTY has higher degree of covalent crosslinking with better aggregation ability of α-, γ-gliadin, and low molecular weight glutenin subunits than frozen dough with yeast. Chemical analysis and chain morphology results demonstrated that the levels of acidity, NH₂, and free sulfhydryl in dough were decreased, and the protein molecules aggregated into longer chains when using PTY instead of yeast, indicating that PTY reduced acid-mediated hydrolysis and increased the disulfide bonds-mediated gluten polymerization.

Frozen steamed breads and boiled noodles: Quality affected by ingredients and processing

Chinese steamed breads (CSB) and noodles are staple foods for many people. The production of frozen steamed products and boiled noodles has kept increasing. This is due to the increasing demand of ready-to-eat frozen food products from the market. Frozen storage significantly increases the self-life of the products and reduces the production costs. On the other hand, the freezing and frozen storage lead to quality loss of the frozen products. This review summarizes effects of freezing and frozen storage on diverse quality attributes (e.g., structural and textural properties) of frozen northern-type steamed breads and boiled noodles. Food safety of the frozen products related to the COVID-19 pandemic is discussed. To counteract the quality loss of the frozen products, suitable processing methods, selection of basic ingredients and uses of various food additives can be done. Research gaps to improve the textural, cooking and nutritional quality of frozen CSB and noodles are suggested.