Genomic region and origin for selected traits during differentiation of small-fruit cultivars in Japanese apricot (Prunus mume).

The Japanese apricot (Prunus mume) is a popular fruit tree in Japan. However, the genetic factors associated with fruit trait variations are poorly understood. In this study, we investigated nine fruit-associated traits, including harvesting time, fruit diameter, fruit shape, fruit weight, stone (endocarp) weight, ratio of stone weight to fruit weight, and rate of fruit gumming, using 110 Japanese apricot accessions over four years. A genome-wide association study (GWAS) was performed for these traits and strong signals were detected on chromosome 6 for harvesting time and fruit diameters. These peaks were shown to undergo strong artificial selection during the differentiation of small-fruit cultivars. The genomic region defined by the GWAS and XP-nSL analyses harbored several candidate genes associated with plant hormone regulation. Furthermore, the alleles of small-fruit cultivars in this region were shown to have genetic proximity to some Chinese cultivars of P. mume. These results indicate that the small-fruit trait originated in China; after being introduced into Japan, it was preferred and selected by the Japanese people, resulting in the differentiation of small-fruit cultivars.

Carbon stable isotopic compositions of citric acid and malic acid in Japanese apricot liqueur decrease as the fruit ripens.

The carbon stable isotopic composition (δ13C) is often analyzed to quantify the addition of acidulants to Japanese apricot liqueur, but little is known about the variation in the δ13C values of the main organic acids arising from differences in the ripeness of Japanese apricots. We show that in Japanese apricot liqueur prepared using fruits at different stages of ripeness, the δ13C values of citric acid and malic acid ranged from -25.1‰ to -23.7‰ and from -22.3‰ to -19.7‰, respectively, and the δ13C values decreased as the fruit ripened. The average δ13C value of citric acid from liqueurs was 0.7‰ higher than that from fresh fruits, whereas the δ13C values of malic acid showed no isotope discrimination. The variation in δ13C values of the main organic acids in Japanese apricot liqueurs will help detect acidulant addition and control authenticity.

Application of carbon and hydrogen stable isotope analyses to detect exogenous citric acid in Japanese apricot liqueur.

Japanese apricot liqueur manufacturers are required to control the quality and authenticity of their liqueur products. Citric acid made from corn is the main acidulant used in commercial liqueurs. In this study, we conducted spiking experiments and carbon and hydrogen stable isotope analyses to detect exogenous citric acid used as an acidulant in Japanese apricot liqueurs. Our results showed that the δ13C values detected exogenous citric acid originating from C4 plants but not from C3 plants. The δ2H values of citric acid decreased as the amount of citric acid added increased, whether the citric acid originated from C3 or C4 plants. Commercial liqueurs with declared added acidulant provided higher δ13C values and lower δ2H values than did authentic liqueurs and commercial liqueurs with no declared added acidulant. Carbon and hydrogen stable isotope analyses are suitable as routine methods for detecting exogenous citric acid in Japanese apricot liqueur.

Method for the isolation of citric acid and malic acid in Japanese apricot liqueur for carbon stable isotope analysis.

A method for detecting the undeclared addition of acidic ingredients is required to control the authenticity of Japanese apricot liqueur. We developed an analytical procedure that minimizes carbon isotope discrimination for measurement of the δ(13)C values of citric and malic acid isolated from Japanese apricot liqueur. Our results demonstrated that freeze-drying is preferable to nitrogen spray-drying, because it does not significantly affect the δ(13)C values of citric acid and results in smaller isotope discrimination for malic acid. Both 0.1% formic acid and 0.2% phosphoric acid are acceptable HPLC mobile phases for the isolation of citric and malic acid, although the δ(13)C values of malic acid exhibited relatively large variation compared with citric acid following isolation using either mobile phase. The developed procedure allows precise δ(13)C measurements of citric and malic acid isolated from Japanese apricot liqueur.

Phenolics profile of mume, Japanese apricot (Prunus mume Sieb. et Zucc.) fruit.

The fruit of mume, Japanese apricot (Prunus mume Sieb. et Zucc.), was evaluated for its phenolics content, high performance liquid chromatography (HPLC) profile and antioxidative activities. The phenolics content of mume fruit was relatively high, the flesh of fully matured fruit containing up to 1% of phenolics on a dry weight basis. Reflecting such a high content of phenolics, the ORAC (oxygen radical absorbance capacity) value for mume fruit flesh showed high values, ranging from 150 to 320 µmol/g Trolox equivalent, depending upon the stage of maturation. 5-O-Caffeoylqunic acid (chlorogenic acid), 3-O-caffeoylquinic acid and tetra-O-acylated sucrose-related compounds were isolated from the flesh of mume fruit, although many unknown peaks were also apparent in the HPLC chromatogram. An alkali hydrolysate comprised four main phenolic acids, caffeic acid, cis/trans-p-coumaric acid and ferulic acid. No flavonoids were observed in the analysis. These results suggest that the majority of phenolics in mume fruit were hydroxycinnamic acid derivatives.