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The colour quality and functional activity of dried fruits are important quality indexes. The purpose of this study was to evaluate the effects of heat pump drying with different air velocity on browning‐related reactions and antioxidant activities of products and their storage counterparts. The results showed that apple cubes possessed different Maillard reaction levels, polyphenol and pectin variation, and antioxidant capacity, which could be controlled by different drying air velocity when the temperature is constant. In present work, high air velocity (2.0–2.5 m/s) drying (HHD) apple cubes possessed 22.58% more browning comparing to low air velocity (0.02–0.50 m/s) drying (LHD), which correlated with its 8.13 μg/g, 132.35 μg/g and 6.21% more of 5‐HMF, chlorogenic acid and DE level of pectin, respectively. Interestingly, the b value of HHD and LHD samples decreased after storage, which was related to the DE, GalA, structural properties (Ratio1, Ratio2 and Ratio3) and conformational properties (PDI, RG and RC) of pectin in samples. Besides, HHD treatment promoted higher DPPH and FRAP capacity than LHD, which significantly involved Mw of pectin. The research would provide a new insight from the perspective of pectin for regulating the browning and antioxidant activity in apple thermal process. [ABSTRACT FROM AUTHOR]

Maillard reaction browning is one of the quality deterioration in dried fruit products, but how pectin affects Maillard reaction in the fruit drying and storage process is not clear. This study aimed at investigating the mechanism of pectin variation impact on the browning of Maillard reaction by using simulated system (l -lysine, d -fructose and pectin) in thermal (60 °C and 90 °C for 8 h) and storage (37 °C for 14 days) process. Results showed that apple pectin (AP) and sugar beet pectin (SP) significantly enhanced the browning index (BI) of the Maillard reaction system by 0.01 to 134.51 in the thermal and storage processes, respectively, which were methylation degree of pectin-dependent. The pectin depolymerization product participated Maillard reaction by reacting with l -lysine, and increasing the 5-hydroxymethyl furfural (5-HMF) content (1.25–11.41-fold) and Abs 420nm (0.01–0.09). It also produced a new product (m / z 225.1245), which finally increased browning level of the system. [Display omitted] • Pectin improved Maillard reaction system browning in the processing. • The effect of pectin on Maillard reaction browning was pectin structure-dependent. • Pectin promoted the accumulation of Maillard reaction products. • Maillard reaction system with pectin produced a new product (m / z 225.1245). • The degradation of pectin with different molecular properties was different. [ABSTRACT FROM AUTHOR]

Browning of some processed fruit products was affected not only by polyphenol oxidation but also by cell wall polysaccharides (pectin). The study was performed to understand the mechanism of browning in the pectin system. The catechin/chlorogenic acid oxidation system in three pectins significantly enhanced their browning during thermal storage with pectin structure- and concentration-dependent. Particularly, the structural and physicochemical properties of pectin were examined to determine its effects on the kinetics of polyphenol oxidation and the stability of free polyphenols. Moreover, pectin impacted the fluorescence characteristics of polyphenols by cross-linking with the aromatic ring of polyphenols. In turn, the interaction between polyphenols and pectin impacted the chemical bond vibration of pectin, thereby affecting its optical features and browning. The correlation analysis revealed that the monosaccharide composition, Ratio 1, Ratio 2, Ratio 3, methyl esterification, ζ-potential, and polydispersity index of pectin were significantly correlated with the browning of the pectin-polyphenol oxidation system. [Display omitted] [ABSTRACT FROM AUTHOR]

Pectin is an important active polysaccharide in the matrix of dried fruit slices. Its components and structural character not only affect the texture but also impact the color of the dried fruit products. Present work studied the variation of pectin fractions of water-soluble (WSP), trans -cyclohexane-1,2-diaminetetraacetic acid-soluble (CSP), and sodium carbonate-soluble (NSP) from apple slices dried by using freeze-drying (FD), 60 °C hot air drying (HAD60), and 90 °C hot air drying (HAD90), to investigate the correlation of their monosaccharide composition, molecular weight distribution, Fourier transform infrared (FTIR) spectrum and small-angle X-ray scattering (SAXS) intensity plot of pectin fractions with the appearance browning of the apple slices. It was found that thermally process ruptures the cell wall structure and pectin component, leading to 12.57% less yield of WSP, and a maximum of 6.35% more yield of NSP pectin fractions. In FD, HAD60, and HAD90 apple slices, the linearity of WSP decreased but the branching extent of the rhamnogalacturonan I (RG-I) domain of WSP and NSP increased successively. The weight average molecular mass (Mw) and number average molar mass (Mn) of WSP and NSP increased as drying temperature increased, whereas they decreased in CSP. The thermal treatment promoted the dehydration of the pectin and caused higher methyl esterification, inducing the structure of pectin more compact and tighter. Moreover, the pectin structural characteristics of the degree of esterification (DE), the radius of gyration (Rg) value, conformational index (ν), and galactose content of three soluble pectin fractions were positively correlated with the a* and b* value of different dried apple slices. [Display omitted] • Different drying techniques induce different changes in three pectin fractions. • The change of pectin fractions notably impacts the browning of dried apple slices. • Thermal treatment induced methyl esterification of pectin fractions of dried apple. • Thermal treatment made the structure of pectin much more compact and tighter. [ABSTRACT FROM AUTHOR]