Byeong Hyeon Yun

This study investigated developmental changes in phenolic compounds and condensed tannin structure in the berry skins of three table grape cultivars, ‘Rosetta’ (RT), ‘Shooting Star’ (SS), and ‘Hongju Seedless’ (HS), from flowering to harvest. Spectrophotometric analyses were used to quantify total phenolic, proanthocyanidin, polymeric tannin, and anthocyanin contents, while high-performance liquid chromatography coupled with thioacidolysis was applied to characterize flavan-3-ol composition and determine the mean degree of polymerization (mDP) of condensed tannins. Phenolic accumulation exhibited distinct cultivar-dependent developmental patterns. Total phenolics and flavan-3-ol monomers generally decreased as berries matured, whereas anthocyanins accumulated after veraison in RT and HS. Polymeric tannins increased during the early developmental stage and subsequently declined, while mDP showed an overall tendency to increase toward maturity, particularly in RT, although the effects of cultivar, developmental time, and their interaction on mDP were not statistically significant. HS maintained high flavan-3-ol concentrations during early development, whereas SS exhibited comparatively low phenolic accumulation together with relatively limited variation in mDP. These findings provide the first comprehensive characterization of developmental changes in flavan-3-ol composition, polymeric tannin structure, and mDP in newly developed Korean table grape cultivars and a structural basis for understanding cultivar-dependent phenolic changes during berry development.

Condensed tannin affecting astringency in grapes maturated and growing were determined qualitatively and quantitatively using reversed-phase high performance liquid chromatography (HPLC). 7 monomeric and 2 dimeric tannin procyanidin B1 and B2 standards were respectively separated in retention time 42 min. Samples divided in berry, flesh and skin were extracted with each other way to compare qualitative and quantitative grape tannin contents. Grape berry and flesh after crushing softly likewise chewing grape were mixed with 70% acetone buffer shortly and filtered, skin stirring extracted for 2 hours. Tannin purified from anthocyanin and other organic compounds such as carbohydrates or organic acids with open column elution for HPLC injection. In all grape samples matured and growing were found completely catechin and dimeric procyanidin B1. Condensed tannin in grape skin were detected in higher concentration than in grape berry and flesh. Just like stirring extraction, only blending and scrambling with organic solvent could be detect tannin in obvious concentration. Because separation of the monomeric tannin from the polymeric in grape skin increases after extractions time, the detection of tannin will be larger. Therefore, the grape berry extraction after shortly scrambling could be used effectively for the determination of grape tannin contents affecting astringency.

Jeong-Sil Choi, Youn-Young Hur, Byeong-Hyeon Yun, Jung-Ho Noh, and Dongjun Im. Journal of the Korean Society of Food Science and Nutrition 2024;53:1185-92. https://doi.org/10.3746/jkfn.2024.53.11.1185

Extensive research has been conducted on the in vitro mass propagation of pear (Pyrus spp.) trees through vegetative propagation, demonstrating high efficiency in shoot multiplication across various pear species. However, the low in vitro rooting rates remain a significant barrier to the practical application and commercialization of mass propagation. This study aims to determine the favorable conditions for inducing root formation in the in vitro microshoots of Pyrus genotypes. The base of the microshoots was exposed to a high concentration (2 mg L⁻¹) of auxins (a combination of IBA and NAA) for initial root induction at the moment when callus formation begins. The microshoots were then transferred to an R1 medium (1/2 MS with 30 g L⁻¹ sucrose without PGRs) to promote root development. This method successfully induced rooting in three European pear varieties, one Asian pear variety, and a European–Asian hybrid, resulting in rooting rates of 66.7%, 87.2%, and 100% for the European pear (P. communis), 60% for the Asian pear (P. pyrifolia), and 83.3% for the hybrid pear (P. pyrifolia × P. communis) with an average of 25 days. In contrast, the control group (MS medium) exhibited rooting rates of 0–13.3% after 60 days of culture. These findings will enhance in vitro root induction for various pear varieties and support the mass propagation and acclimatization of pear. The in vitro root induction method developed in this study has the potential for global commercial application in pear cultivation.