Influence of ε-poly-l-lysine treated yeast on gluten polymerization and freeze-thaw tolerance of frozen dough

Alleviative effects of phosphates on quality deterioration of frozen dough during freeze-thaw cycles: A focus on gluten aggregation and dough fermentation

This study investigated the effects of phosphates on the quality of frozen steamed bread, focusing on rheological properties, water status, fermentation characteristics, and protein aggregation properties. The findings revealed that phosphates significantly improved the quality of frozen steamed bread. After 3 freeze-thaw (F/T), the specific volumes of 0.6 % sodium tripolyphosphate (STPP) and 0.4 % sodium hexametaphosphate (SHMP) samples increased by 17.65 % and 20.32 %, respectively, compared to the control. Hardness decreased by 38.12 % and 24.55 %, respectively, while internal porosity of the 0.6 % STPP and SHMP samples improved by 32.37 % and 21.76 %, respectively. Furthermore, phosphates enhanced dough elasticity and viscosity, effectively inhibiting water migration and reducing freezable water content. Yeast gas production also increased after F/T, as phosphates improved yeast tolerance by moderately slowing yeast growth. Notably, phosphates mitigated glutenin macropolymer (GMP) depolymerization by inhibiting yeast to reduce reductant production during F/T cycles. Phosphates also contributed to a more stable protein secondary structure. In conclusion, phosphates played a crucial role in alleviating the quality deterioration of frozen dough by influencing protein aggregation, thereby offering novel insights into their benefits for dough-based products.

Revealing the Cryoprotective Mechanism of Wheat Bran Antifreeze Arabinoxylan on Yeast Viability by Metabolite Profiling and Comparative Transcriptome Analysis

To elucidate the cryoprotective mechanism of wheat bran antifreeze arabinoxylan (AX) on yeast cells, this study investigated its effects on the physiological, metabolic, and genetic stability of yeast subjected to cyclic freeze-thaw cycles. Antifreeze AX inhibited ice crystal growth and interacted with cells to form an external barrier, which preserved cell membrane integrity, inhibited reactive oxygen species accumulation, and reduced oxidative damage. Metabolome analysis revealed that AX regulated key metabolic pathways, enhancing cell activity and maintaining homeostasis. Transcriptome analysis demonstrated that AX promoted DNA repair and maintained genetic stability. By synergistically inhibiting ice crystal growth, forming physical barriers and regulating metabolic and genetic pathways, antifreeze AX improved yeast cell viability and activity during freeze-thaw cycles, thereby maintaining cellular homeostasis under freezing stress. This study could provide a theoretical basis for the practical application of antifreeze AX as an efficient cryoprotectant in yeast cell cryopreservation.

Effect of Mixed Yeast Strains and Additives on the Quality of Long-Term Refrigerated Fermented Doughs

With a prolonged refrigeration time, dough becomes syruped and the gluten strength is weakened, which negatively affects the texture of the dough. At the same time, differences in the growth and metabolism of different yeasts lead to large differences in the physicochemical properties of the dough and the final quality of the product. Therefore, in this study, suitable additives and non-Saccharomyces cerevisiae were selected to minimize the effects of long-term refrigeration on the physicochemical properties and microstructure of fermented doughs. Compared to the control group without mixed yeast strains and additives, the fermentation properties, textural properties, dynamic rheology, starch crystallinity, protein structure, water distribution, and microstructure were investigated by mixed yeast strains and additives for 14 days of long-term refrigeration. The results showed that using mixed yeast strains (Saccharomyces cerevisiae: Metschnikowia pulcherrima; Wickerhamomyces anomalous = 0.46:0.27:0.27), α-amylase, diacetyl tartaric acid ester of mono(di)glycerides and polydextrose can avoid the excessive fermentation of refrigerated dough. In addition, mixed yeast strains and additives could maintain the orderliness of the secondary structure of gluten proteins, stabilize the microstructure of starch and gluten proteins, and reduce the migration and loss of water in the dough. This study clarified that mixed yeast strains and additives are conducive to prolonging the long-term refrigeration of dough, and could better maintain the quality of dough during long-term refrigeration. These results provide a theoretical basis for further research on the large-scale production of refrigerated fermented dough.

Revealing the influence mechanism of pre-fermentation degree and storage temperature fluctuations on frozen steamed bread dough quality

This study investigated the effects of pre-fermentation degree and storage temperature fluctuations on the gas cells, gluten protein, rheological properties of frozen dough, and quality of steamed bread. Three pre-fermentation degrees and four fluctuating temperatures (-10 °C, 0 °C, 10 °C, and 25 °C) were used. The gas cell size increased with the pre-fermentation degree; however, the gas cells merged and ruptured during temperature fluctuations. Sodium dodecyl sulfate extraction protein content and free sulfhydryl content increased by 3.07 % and 33.62 %, respectively, in the medium pre-fermentation group at 25 °C compared with those at -10 °C. The maximum strain of dough increased as pre-fermentation degree and fluctuating temperatures increased. The specific volumes of steamed bread with medium pre-fermentation degree were 1.87 mL/g at -10 °C and 1.47 mL/g at 25 °C. In conclusion, higher temperature fluctuations exceeding the freezing point exacerbated the dough and steamed bread quality, particularly in high pre-fermentation degree dough.

Selenium-enriched yeast, a selenium supplement, improves the rheological properties and processability of dough: From the view of yeast metabolism and gluten alteration

This study investigated the effect mechanism of selenium (Se)-enriched yeast on the rheological properties of dough from the perspective of yeast metabolism and gluten alteration. As the yeast Se content increased, the gas production rate of Se-enriched yeast slowed down, and dough viscoelasticity decreased. The maximum creep of Se-enriched dough increased by 29%, while the final creep increased by 54%, resulting in a softer dough. Non-targeted metabolomics analyses showed that Se inhibited yeast energy metabolism and promoted the synthesis of stress-resistance related components. Glutathione, glycerol, and linoleic acid contributed to the rheological property changes of the dough. The fractions and molecular weight distribution of protein demonstrated that the increase in yeast Se content resulted in the depolymerization of gluten. The intermolecular interactions, fluorescence spectrum and disulfide bond analysis showed that the disruption of intermolecular disulfide bond induced by Se-enriched yeast metabolites played an important role in the depolymerization of gluten.

Insight into konjac glucomannan-retarding deterioration of steamed bread during frozen storage: Quality characteristics, water status, multi-scale structure, and flavor compounds

Konjac glucomannan (KGM), a water-soluble hydrocolloid, holds considerable potential in the food industry, especially for improving the quality and nutritional properties of frozen products. This study explored the alleviative effect of KGM on the quality characteristics, water status, multi-scale structure, and flavor compounds of steamed bread throughout frozen storage. KGM significantly improved the quality of steamed bread by slowing down the decrease in water content and the increase in water migration while maintaining softness and taste during frozen storage. Notably, KGM also delayed amylopectin retrogradation and starch recrystallization, thus preserving the texture and structure of the steamed bread. At week 3, the microstructure of the steamed bread with 1.0 % KGM remained intact, with the lowest free sulfhydryl content. Additionally, heat map analysis revealed that KGM contributed to flavor retention in steamed bread frozen for 3 weeks. These results indicate that KGM holds promise as an effective cryoprotectant for improving the quality of frozen steamed bread.

Effects of freeze-thaw cycles on the quality of Hot-dry noodles: From the moisture, starch, and protein characteristics

Freeze-thaw cycles (FTC) could cause damage to food during storage. The effects of different FTC on Hot-dry noodles (HDN) in terms of quality, moisture, starch, and protein characteristics were studied. This study showed that FTC decreased the texture properties and water absorption of HDN. Meanwhile, cooking loss was significantly increased after FTC. The water content of HDN was decreased and water migration was increased during FTC. In addition, results showed that FTC destroyed the order structure and increased the crystallinity of starch in HDN. Under FTC, the disulfide bond of HDN was broken, the free sulfhydryl group was increased, and the electrophoretic patterns confirmed the protein depolymerization. The microstructure also showed that the gluten network became incomplete and starch was exposed outside the substrate. This study expounded the mechanism of HDN quality deterioration during FTC, which laid a foundation for the development and improvement of frozen and freeze-thaw noodles.

Effects of improver on the quality of frozen Chinese sweet rice wine dough: Water status, protein structure and flavor properties

In the study, a sweet wine koji (YQ-5) was successfully selected to make frozen Chinese sweet rice wine dough (F-CD) for flavor enrichment. Subsequently, the effects of single improver (SI: xanthan gum, potassium carbonate, antifreeze protein, diacetyl tartaric esters of monoglycerides and composite improver (XPADG: Four improvers mixed in proportion) on the texture, rheological properties, microstructure, water status, protein secondary structure, volatile flavor substances and sensory properties of F-CD during frozen storage were investigated. The results indicated that XPADG slowed the increase in freezable water and water mobility in the dough, giving dough the most stable rheological properties and minimizing the damage of freezing to the secondary structure and microstructure of proteins. Besides, GC-QTOF/MS analysis showed that XPADG may facilitate the retention of flavoring substances in F-CD after storage for 6 days. Finally, the sensory evaluation showed that XPADG imparted good sensory properties to the product after freezing for 6 days.

Quality analysis of dough and steamed bread under various freezing conditions

Freezing is a crucial step in the process of frozen foods. In this study, the effects of different freezing methods, including liquid nitrogen immersion freezing (LF), quick-freezing machine freezing (QF), packaging immersion freezing (PF), and ultralow temperature refrigerator freezing (UF), and freezing time (0, 15, 30, and 60 days) on the textural properties, dynamic rheological properties, water distribution, and structure of dough and the quality of end steamed bread were evaluated. Freezing resulted in a decline in the physicochemical properties of dough. UF- and QF-doughs had higher storage modulus and loss modulus, compared with PF- and LF-doughs. LF enhanced the textural attributes of the dough, resulting in reduced hardness and increased springiness. At 15 days of freezing, QF- and LF-doughs exhibited a compact and continuous structure with a smooth surface. Additionally, the correlation analysis elucidated that the weight loss rate and the bound water content of the dough had discernible impacts on the texture of both the dough and the resulting steamed bread. Overall, LF demonstrated a relatively high freezing efficiency and effectively maintained the quality of the dough for up to 15 days of freezing. These results offer valuable insights for the applications of freezing methods and time in frozen foods.

Understanding the mechanism for sodium tripolyphosphate in improving the physicochemical properties of low-moisture extrusion textured protein from rapeseed protein and soybean protein blends

Our previous experiments found that rapeseed protein (RP) has applicability in low-moisture textured proteins. The amount of RP added is limited to <20 %, but the addition of 20 % RP still brings some negative effects. Therefore, in order to improve the quality of 20%RP textured protein, this experiment added different proportions of sodium tripolyphosphate (STPP) to improve the quality of the product, and studied the physical-chemical properties and molecular structure changes of the product to explore the possible modification mechanism. The STPP not only improved the expansion characteristics of extrudates, but also increased the brightness of the extrudates, the rehydration rate. In addition, STPP increased the specific mechanical energy during extrusion, decreased the material mass flow rate. Furthermore, STPP decreased the starch digestibility, increased the content of slow-digesting starch and resistant starch. STPP increased the degree of denaturation of extrudate proteins, the proportion of β-sheets in the secondary structure of proteins, as well as the intermolecular hydrogen bonding interactions. The gelatinization degradation degree of starch molecules also decreased with the addition of STPP. STPP also increased the protein-starch interactions and enhanced the thermal stability of the extrudate. All these indicate that STPP can improve the physical-chemical properties of extrudate.

Alleviative effects of mannosylerythritol lipid-A on the deterioration of internal structure and quality in frozen dough and corresponding steamed bread

The effects of mannosylerythritol lipid-A (MEL-A) on the quality of frozen dough and corresponding steamed bread were investigated. The results revealed that the rheological properties of frozen dough were improved with the increment of MEL-A (0%-2.0%). Adding 1.5% and 2% MEL-A significantly reduced the moisture migration and enhanced the water-holding capacity of the frozen dough. Microstructure observation demonstrated that high levels of MEL-A enabled more starch granules to be embedded in the dough network. A series of product quality assessments illustrated that frozen dough steamed bread containing 2.0% of MEL-A had the largest specific volume (2.981 mL/g), the highest springiness (77.47%), more uniform and porous crumb structure. Moreover, MEL-A exhibited a positive effect on steamed bread's flavor profile, which was explored for the first time in this study. Hence, these results suggested that MEL-A has promising applications as a novel dough improver in the food industry.

Effect of different enzymes on thermal and structural properties of gluten, gliadin, and glutenin in triticale whole-wheat dough

Three enzymes promoted the development of the gluten network in triticale whole-wheat noodles (TWWN). To further understand the mechanism of gluten enhancement, the effects of three enzymes on the structure of gluten and its fractions (gliadin and glutenin) were evaluated. The results showed that glucose oxidase (GOD), xylanase (XYL), and laccase (LAC) decreased the content of sodium dodecyl sulfate (SDS) extractable proteins. The content of glutenin subunits was reduced by 17.25 %, 30.60 %, and 20.09 % with the addition of GOD, XYL, and LAC, respectively. Furthermore, GOD and LAC increased the content of glutenin macropolymer (GMP) by 2.64 % and 7.71 %, respectively, suggesting the promotion of glutenin aggregation. The addition of three enzymes decreased the weight loss and increased the degradation temperature of the gluten and its fractions. GOD and XYL decreased the fluorescence intensity of gluten and its fractions, except for XYL which increased the fluorescence intensity of glutenin by 10.50 %. Intermolecular interactions and surface hydrophobicity were enhanced by XYL in gluten and its fractions. GOD and LAC decreased the free sulfhydryl content and increased the β-sheet content, suggesting that the covalent interaction between gluten fractions was enhanced. Therefore, this research can enrich the theoretical study of enzymatic cross-linking.

Insight into curdlan alleviating quality deterioration of frozen dough during storage: Fermentation properties, water state and gluten structure

Curdlan was effective in alleviating quality deterioration of frozen dough during storage. This research explored the mechanisms from perspectives of fermentation properties, water state and gluten structure of frozen dough during storage, and the performance of corresponding steamed bread. Results showed that curdlan addition improved the gas-releasing capability and gas-holding capability of frozen dough, meanwhile enhanced the specific volume and textural properties of corresponding steamed bread. The melting enthalpy and NMR results demonstrated that curdlan restricted the conversation of bound water into freezable water, and inhibited the moisture migration in frozen dough. Frozen dough with 0.5% curdlan had significantly lower gluten macropolymers (GMP) depolymerization degree and free sulfhydryl (SH) content than the control, indicating that curdlan alleviated the depolymerization of GMP. Microstructure results proved that the deterioration of the structure was retarded by curdlan. This study contributes to understanding the theories for curdlan alleviating the deterioration of frozen dough during storage.

Effect of Lactylated Gluten and Freeze-Thaw Cycles on Frozen Dough: From Water State and Microstructure

The influence of lactylated gluten and Freeze-Thaw Cycles on the water state, microstructure, and quality of frozen steamed bread dough was investigated. After three freeze-thaw cycles (3F/T), the specific volume of steamed bread with sodium lactate-treated gluten increased by 18.34% compared with the blank group and 5.73% compared with the wheat gluten (WG) group. Compared with wheat gluten, the texture properties of steamed bread with lactylated gluten increased significantly. Changes in rheological properties demonstrated that the frozen dough's viscoelasticity increased significantly. The lactylated gluten could reduce water mobility and decrease the content of freezable water in frozen dough. Moreover, the free sulfhydryl (SH) content increased, revealing that the protein was depolymerized. Based on the microstructure and corresponding protein network analysis (PNA), the total area and the number of protein network connection points of the dough adding lactylated gluten were significantly higher than those of the blank group and the WG group. In conclusion, lactylated gluten enhanced the freeze-thaw tolerance of frozen dough.

Impact of Different Frozen Dough Technology on the Quality and Gluten Structure of Steamed Buns

To advance the industrialization production of steamed buns, the current study explored the freeze-stability of unfermented, pre-fermented and par-steamed frozen dough. The results showed that the steamed bun made from unfermented dough with 2.0% yeast, the pre-fermented dough with a pre-fermented time of 30 min and the par-steamed dough with a pre-steamed time of 15 min showed the best sensory properties quality upon frozen storage. The gassing power of un- and pre-fermented dough gradually decreased, and dough with longer pre-fermented time exhibited more evident loss of gassing power. Freeze-induced depolymerization of gluten protein was the least distinct in the par-steamed dough, followed by the pre- and un-fermented dough, which was probably related to the superior freeze stability of glutenin-gliadin macro-crosslinks upon the pre-steaming stage. The surface hydrophobicity of gluten proteins of frozen dough decreased during the initial storage and was enhanced subsequently, which was related with the combined effects of the unfolding and synchronous aggregation induced by freezing and steaming, respectively. Moreover, the surface hydrophobicity of gluten in par-steamed frozen dough and steamed buns was more resistant to frozen storage, which was probably attributed to the established stable structure during the pre-steaming process.

Egg white protein addition induces protein aggregation and fibrous structure formation of textured wheat gluten

The effect of egg white protein addition on the fibrous structure and protein aggregation of textured wheat gluten (TWG) extrudates was investigated. The hardness, springiness, chewiness, and degree of texturization of TWG significantly increased with the addition of egg white protein. Analysis of morphological characteristics showed a positive effect of egg white protein on the formation of the fibrous structure of TWG. The results of size-exclusion high performance liquid chromatography (SE-HPLC) indicated that the egg white protein improved the degree of wheat gluten aggregation, and the analysis of the protein intermolecular forces proved that disulfide bonds were the main contributor to the cross-linking of protein. In addition, an increase in the β-sheets also indicated an increase in protein aggregation induced by egg white protein. The addition of egg white protein promoted protein interactions and improved the fibrous structure of TWG.

Recent development in evaluation methods, influencing factors and control measures for freeze denaturation of food protein

Frozen storage is most widely adopted preservation method to maintain food freshness and nutritional attributes. However, at low temperature, food is prone to chemical changes such as protein denaturation and lipid oxidation. In this review, we discussed the reasons and influencing factors that cause protein denaturation during freezing, such as freezing rate, freezing temperature, freezing method, etc. From the previous literatures, it was found that frozen storage is commonly used to prevent freeze induced protein denaturation by adding cryoprotectants to food. Some widely used cryoprotectants (for example, sucrose and sorbitol) have been reported with higher sweetness and weaker cryoprotective abilities. Therefore, this article comprehensively discusses the new cryopreservation methods and providing comparative study to the conventional frozen storage. Meanwhile, this article sheds light on the freeze induced alterations, such as change in functional and gelling properties. In addition, this article could be helpful for the prolonged frozen storage of food with minimum quality related changes. Meanwhile, it could also improve the commercial values and consumer satisfaction of frozen food as well.

Understanding how starch constituent in frozen dough following freezing-thawing treatment affected quality of steamed bread

Understanding how starch constituent in frozen dough affected bread quality would be valuable for contributing to the frozen products with better quality. To elucidate the underlying mechanism, starch was fractionated from multiple freezing-thawing (F/T) treated dough and reconstituted with gluten. Results showed that F/T treatment destructed the molecular and supramolecular structures of starch, which were more severe as the F/T cycle increasing. These structural disorganizations made water molecules easier to permeate into the interior of starch granules and form hydrogen bonds with starch molecular chains, which elevated the peak, breakdown, setback and final viscosity of starch paste. In addition, F/T treatment resulted in decreased specific volume (from 1.54 to 0.90 × 10³ m³/Kg) and increased hardness (from 42.98 to 52.31 N) for steamed bread. We propose the strengthened water absorption ability and accelerated intra- and inter-molecular rearrangement of starch molecules and weak stability of "starch-gluten matrices" would allow interpreting deteriorated bread quality.

Effect of NaHCO3 and freeze-thaw cycles on frozen dough: From water state, gluten polymerization and microstructure

This study investigated the influence of NaHCO₃ on the water state, gluten polymerization, microstructure and quality of frozen steamed bread dough during freeze-thaw cycles. Results showed that the steamed bread made from alkaline (0.4% NaHCO₃) frozen dough possessed a larger specific volume and smaller hardness after 4 freeze-thaw cycles, than the non-alkaline dough group. The addition of NaHCO₃ slowed the increase of freezable water content and water mobility of dough during freeze-thaw cycles, and the high amount of NaHCO₃ (0.4%-1%) showed the great effect. Compared with non-alkaline dough, the sodium dodecyl sulfate extractable protein proportion and free sulfhydryl level of alkaline dough increased less after freeze-thaw cycles, indicating a strengthened freeze-thaw tolerance of alkaline dough. Based on microstructure image and corresponding protein network analysis (PNA) results, the protein area and total protein length in alkaline dough remained at a higher level than non-alkaline group after 4 freeze-thaw cycles.