The formation pattern of off-flavor compounds induced by water migration during the storage of sea cucumber peptide powders (SCPPs)

Effect of ultra-high pressure combined with heat-assisted treatment on the characterization, moisture absorption, and antioxidant activity properties of walnut peptide

In this study, ultra-high pressure (UHP) and heat-assisted technology (HT) were used to process walnut peptides (WP) and investigate their combined effects (UHP-HT) on the characterization, moisture absorption, and antioxidant activity of WP. The results indicated that UHP (300 Mpa, 10 min) combined with HT treatment (55 °C, 30 min) significantly increased the surface hydrophobicity and disulfide bonds of WP. UHP-HT-treated WP exhibited lower moisture absorption and more stable water molecule migration. Additionally, the moisture absorption capacity of the WP (48.78 %) was significantly decreased in WP-UHP, WP-HT and WP-UHP (45.37 %, 43.15 %, and 40.19 %, respectively) because of increasing the surface hydrophobicity. UHP-HT combined improved structural characteristics, including particle size, zeta potential, and functional group stability, and significantly enhanced the antioxidant activity of WP under high humidity conditions. Overall, these findings suggest that UHP-HT can effectively reduce the moisture absorption of WP, thus enhancing its storage stability and extending its shelf life.

The possible inhibition mechanism of low salt dry-curing on volatile flavor deterioration in refrigerated grass carp (Ctenopharyngodon idella) blocks: Metabolomics and microorganisms

Complex microbial communities have an important impact on the flavor of low salt dry-curing (LSD)-pretreated grass carp blocks. Here, the flavors, metabolites, and bacterial diversity of LSD-pretreated fish during cold storage were analyzed using flavor analysis, metabolomics, and high-throughput sequencing to investigate their correlations in detail. LSD promoted the volatile flavor deterioration of grass carp blocks under 6 days of refrigeration but inhibited it under 15 days of refrigeration. Furthermore, 924 metabolites were identified in the refrigerated grass carp blocks, and LSD inhibited the growth of Psychrophilic dominant spoilage microorganisms (Proteobacteria) and promoted microbial abundance (Actinobacteriota, Firmicutes, Bacteroidota, and Cyanobacteria). Correlation analysis revealed that the degradation of phosphatidylcholine connected with the monomonas genus in LSD-pretreated fish blocks played a vital role in inhibiting the key volatile flavor (esters, aldehydes, and alcohols) deterioration. This information is useful for elucidating the inhibition mechanism of LSD on flavor deterioration in refrigerated fish blocks.

The moisture adsorption, caking, and flowability of silkworm pupae peptide powders: The impacts of anticaking agents

This study aimed to explore the impacts of different anticaking agents on the moisture adsorption, caking, and flowability of silkworm pupae peptide powders (SPPP). The characteristics of water distributions in SPPP with anticaking agents were investigated by LF NMR. The morphological observation of powders was analyzed by scanning electron microscope. Moisture sorption curves and moisture sorption isotherm curves indicated that calcium stearate, silicon dioxide and calcium silicate of 20 % reduced hygroscopicity and increased critical relative humidity. The angle of repose analysis revealed that anticaking agents could also increase flowability (45°-49°). LF NMR analysis indicated that anticaking agents reduced the moisture adsorption ability of SPPP. Scanning electron microscope observations demonstrated different shapes and surface morphology of SPPP using different anticaking agents. Notably, silicon dioxide served as the most effective anticaking agent by forming a physical barrier. Overall, anticaking agents can effectively delay moisture adsorption and deliquescence of SPPP by different anticaking fashions.

Analysis of Volatile Flavor Substances in the Enzymatic Hydrolysate of Lanmaoa asiatica Mushroom and Its Maillard Reaction Products Based on E-Nose and GC-IMS

An electronic nose (E-Nose) and gas chromatography-ion mobility spectrometry (GC-IMS) were used to analyze the volatile flavor compounds (VFCs) of the enzymatic hydrolysate of Lanmaoa asiatica and its Maillard reaction products (MRPs). E-Nose sensors have strong response signals to sulfide, nitrogen oxides, alcohols, and aldehyde ketone, and the aroma profile was increased after the Maillard reaction (MR). According to GC-IMS, A total of 84 known compounds were identified. Aldehydes, ketones and alcohols are the main VFCs. After MR, the concentrations of some alcohols decreased, and the concentration of pyrazines and ketones increased. Principal component analysis (PCA) and similarity analysis showed that the enzymatic hydrolysate and MRPs were different and could be effectively distinguished. In conclusion, this study clarified the changes in VFCs before and after the MR. The results can provide a theoretical basis for the quality control and flavor changes during the processing of Lanmaoa asiatica and provide a new method for flavor analysis of edible mushrooms and their products.

Water distribution and moisture-absorption in egg-white derived peptides: Effects on their physicochemical, conformational, thermostable, and self-assembled properties

Three egg-white derived peptides (DHTKE, MPDAHL, and FFGFN) were characterized with hydrophilia and water distributions. The effect of moisture exposure on their properties at 75% relative humidity for 30 h were further investigated. LF-NMR tests revealed that strong bound-water (relaxation time < 10 ms) accounted for more than 80% of total water in peptides after moisture-absorption. The absorbed water led to the pH of three peptides increase, antioxidant activities in vitro decrease, and diverse changes in their functional group vibrations, molecular hydrophobicity, and phase transformation properties. Compared to dried samples, the hydrated-DHTKE was pyrolyzed and hydrated-MPDAHL was oxidized over 160 °C, while the glass transition, melting, and crosslink temperatures of FFGFN all decreased after moisture-absorption. Moreover, the results indicated that moisture-absorption in FFGFN powder enhanced the surface-hydrophobicity of FFGFN-hydrogel and accelerated its self-organizations. This study provides a comprehensive understanding of moisture-absorption effects on peptides, with these changes potentially impacting storage recommendations and scientific interpretations.

Effects of microwave vacuum drying on the moisture migration, microstructure, and rehydration of sea cucumber

Effectsof microwave vacuum drying (MVD) on moisture migration, microstructure, and rehydration of sea cucumber were investigated in this paper. Vacuum condition avoided the exposure of sea cucumber to high temperature. Low-field nuclear magnetic resonance relaxation results revealed that the peaks of three water components in sea cucumber shifted to short relaxation time during MVD process, and the peak area of major water component-immobilized water-decreased significantly due to water evaporation. Magnetic resonance imaging found that the water in the internal layer of sea cucumber body wall was first removed due to the internal heating of microwave, and then the water in the outer layer. Higher microwave power could promote the moisture transfer motion during drying process, and shorten the drying time. Porous microstructure was observed by Cryo scanning electronic microscope images in sea cucumber dried with microwave power of 200 and 250 W, which might be responsible for high values of rehydration ratio and water holding capacity. High microwave power caused the increase of amino acids content, but had no significant effect on the change of saponins content. In addition, excellent prediction models of moisture ratio have been developed by partial least squares regression analysis based on transverse relaxation data, which proved the feasibility of low-field nuclear magnetic resonance to monitor moisture changes of sea cucumber during MVD process. PRACTICAL APPLICATION: Effects of microwave vacuum drying (MVD) on moisture migration, microstructure, and rehydration of sea cucumber were investigated. Understanding the impacts of MVD drying on water status, texture, and nutritional characteristics of sea cucumber is important to improve the processing quality of dried sea cucumber.

Proton Dynamics of Water Diffusion in Shrimp Hydrolysates Flour and Effects of Moisture Absorption on Its Properties

Moisture absorbed into shrimp hydrolysates (SHs) flour profoundly affected its properties. The unstored hydrolysate flour was called SHs-0h and SHs stored for 30 h at 25 °C and 75% relative humidity was named SHs-30. During the process of storage, the moisture dynamics in SHs flour were investigated by dynamic vapor sorption (DVS) and low-field nuclear magnetic resonance (LF-NMR). The effects of moisture absorption on the radicals scavenging rates of SHs flour were evaluated by electron paramagnetic resonance (EPR). The effects of moisture absorption on secondary structure were studied by mid-infrared (MIR) spectroscopy and infrared microimaging spectroscopy. The changes of volatile components were monitored by purge and trap coupled with gas chromatography-mass spectrometry (PT-GC-MS). DVS results showed that the moisture absorption rate of SHs flour could reach a maximum of 88.93%. Meanwhile, the water was transformed into more stable water with shorter relaxation times. The porous structure of the SHs-30 h flour disappeared and became smoother compared to SH-0 h flour. DPPH (31.09 ± 0.54%) and OH (26.62 ± 1.14%) radicals scavenging rates of SHs-30 h significantly reduced (p < 0.05) compared to that of SHs-0 h flour. The vibrations of the MIR absorbance peaks were changed. Finally, eight volatile components disappeared and six new volatile compounds were found. This study provided a theory basis for moisture dynamics in peptide flour during the storage process.

Flavor Changes of Tricholoma matsutake Singer under Different Processing Conditions by Using HS-GC-IMS

Headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) was used to analyze the changes to volatile compounds in fried Tricholoma matsutake Singer under different heating temperatures and times. A total of 40 signals that corresponded to 24 compounds were identified through this approach. Differences in volatile compounds of T. matsutake samples were shown in topographic plots and fingerprints. The heating temperatures were more important than the heating times in affecting the volatile compounds. Moreover, changes to the main volatile compounds in T. matsutake under different processing conditions were based on the thermal decomposition and a series of chemical reactions of C8 compounds. Principal component analysis (PCA) results showed that samples under different processing conditions could be effectively distinguished. Hence, the combination of HS-GC-IMS and PCA can identify and classify the volatile compounds of T. matsutake quickly and sensitively. This study provides a new supplementary analytical method for the rapid identification of T. matsutake. The above results can provide a theoretical basis for the quality control and change mechanism of flavor in the processing of traditional edible fungi products.

Exploration on self-equilibrium rule and adsorption-desorption model between pine nut (Pinus koraiensis) peptide molecules and environmental moisture molecules

The storage of pine nut (Pinus koraiensis) peptide (PNP) powder involves hygroscopic phenomena. To investigate the adsorption and self-equilibrium rules between these peptides and the environmental moisture molecules, several studies such as low-field nuclear magnetic resonance (LF-NMR), dynamic vapor sorption (DVS) and adsorption-desorption models were done. The results showed that the outward moisture migration occurred during storage as 7.80% and 16.68% moisture were respectively constrained by the original sample and 90 days after lyophilization, by chemical bonding. Additionally, 1.79% moisture was lost in PNP powder at day 90. The optimized adsorption model for PNP powder was changed from Henderson's to Oswin's model during the 90 days' storage whereas the optimized desorption model was changed from Halsey's to GAB's model. The PNP powder at day 90 presented smaller particles with an average diameter and height of 15.645 nm and 50 nm, respectively, and it contained more molecular moisture which cannot be removed. The free thiol of the PNP powder at day 0 and day 90 was 1.75 ± 0.16 μM SH/g and 1.95 ± 0.16 μM SH/g, respectively, and the total sulfhydryl was 101.46 ± 1.06 μM SH/g and 118.44 ± 1.27 μM SH/g. The registered increased sulfhydryl content contributed to the generation of off-flavor.

Mechanism of aroma compounds changes from sea cucumber peptide powders (SCPPs) under different storage conditions

A rapid and sensitive measurement technique was used to investigate the mechanism of aroma compounds changes in SCPPs under the storage conditions with hygroscopicity and no-microorganism (HNM), nonhygroscopicity and no-microorganism (NHNM) and hygroscopicity and microorganism (HM) by HS-GC-IMS. The types and signal of aroma compounds increased obviously at the 5th day under the storage condition (HNM and HM). The signal of majority of aroma compounds decreased gradually since the 5th day. However, during the storage of SCPPs for 15 days, the total signals of aldehydes, ketones and alcohols gradually increased and reached a maximum. Thereinto, the saturated aldehydes such as hexanal had been produced as an off-flavor. These off-flavor compounds principally including aldehydes and ketones could be generated through Maillard reaction, while alcohols could be generated by microbial fermentation. The study discovered moisture adsorption and microorganism during storage could affect aroma compounds of SCPPs and the effect of moisture absorption was greater than microorganisms.