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

Insights into the potential quality markers of Rubus chingii Hu fruit at different growth stages

Rubus chingii Hu fruit (RHF) is a medicinal and edible resource with excellent biological activities. Currently, the existing identification markers can't meet the needs of RHF quality control. This study collected RHF from cultivation fields of three origins [Qiandaohu (QDH), Lishui (LS), and Fuyang (YF)] at green, green to yellow, yellow to orange, and mature stages (G, G to Y, Y to O, M). The physicochemical information of RHF was examined. Water migration and characteristic volatile compounds of RHF at growth stages from different origins were investigated by low field-nuclear magnetic resonance (LF-NMR) technology and gas chromatography-ion mobility spectrometry (GC-IMS) technology. It showed that samples from QDH possessed the highest antioxidant activity at the first three growth stages (e.g.

, DPPH

0.062 ± 0.000, 0.059 ± 0.004 and 0.037 ± 0.002 mmol Trolox/100 g), while FY had the highest at the mature stage (e.g.

, DPPH

0.026 ± 0.001 mmol Trolox/100 g). The total carbohydrates content ranged from 15 % to 43 %. Besides, in the first two stages, the total acidity value was lower (e.g.

, QDH

2.69 ± 0.04 and 2.45 ± 0.04 in g citric acid/L). Furthermore, three origins had the same water migration rule, and finally, 10 compounds, including 5 from the G growth stage, 4 from the G to Y growth stage, and 1 from the Y to O growth stage, were highly correlated with antioxidant activity and can significantly indicate RHF quality from different origins, so they can potentially serve as Q-markers for RHF. Identifying Q-markers provides a research direction for the quality control of RHF, promoting the development of the RHF industry.

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.

Effect of microorganisms on the fingerprint of the volatile compounds in pine nut (Pinus koraiensis) peptide powder during storage

Pine nut (Pinus koraiensis) peptide (PNP) powder possesses promising bioactivities. However, the powder may have the quality problem of becoming sticky and smelly. Therefore, the volatile compounds' fingerprint of PNP powder was established by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). The essential spoilage microorganisms were confirmed by 16S rDNA amplicon sequencing. The antioxidant activity, which presents PNP powder's quality, decreased during storage with the highest value of (1.88 ± 0.18) × 10¹⁴ at day 30. Fifty-nine significantly changed signals were detected; eight compounds were considered as volatile marker compounds. Besides, Firmicutes and Cyanobacteria were the essential spoilage microorganisms in PNP powder at the phylum level. Significantly, unidentified_Chloroplast, which belongs to Cyanobacteria, had a positive correlation with volatile marker compounds. The results proved that microorganisms indeed affect volatile compounds of PNP powder and induced off-flavor, including hexanal, which can be used as the detection indicator for the quality control of PNP powder. PRACTICAL APPLICATIONS: In the present study, we controlled the influence of moisture migration on PNP powder and investigated microorganisms' effects on volatile compounds of PNP powder. HS-GC-IMS could be used to establish fingerprints of volatile compounds in PNP powder. 16S rDNA amplicon sequencing method could be used to screen the dominant spoilage bacteria in PNP powder and established essential spoilage microorganisms of PNP powder. This work provides a reference for category identification of PNP powder, which was infected by spoilage bacteria or not, and stored at day 0 or 30 days. Hexanal can be considered as the volatile marker compound generated from microorganisms. It helps to realize the controllability of PNP powder storage and prolongs the shelf life of PNP powder.