Accumulation Pattern of Amygdalin and Prunasin and Its Correlation with Fruit and Kernel Agronomic Characteristics during Apricot (Prunus armeniaca L.) Kernel Development.

Ping Deng,Yiming Li,Hailan Zhu,Zhong Zhao,Fei Zhao,Buangurn Phommakoun,Bei Cui,Dan Zhang

doi:10.3390/foods10020397

Abstract

To reveal the accumulation pattern of cyanogenic glycosides (amygdalin and prunasin) in bitter apricot kernels to further understand the metabolic mechanisms underlying differential accumulation during kernel development and ripening and explore the association between cyanogenic glycoside accumulation and the physical, chemical and biochemical indexes of fruits and kernels during fruit and kernel development, dynamic changes in physical characteristics (weight, moisture content, linear dimensions, derived parameters) and chemical and biochemical parameters (oil, amygdalin and prunasin contents, β-glucosidase activity) of fruits and kernels from ten apricot (Prunus armeniaca L.) cultivars were systematically studied at 10 day intervals, from 20 days after flowering (DAF) until maturity. High variability in most of physical, chemical and biochemical parameters was found among the evaluated apricot cultivars and at different ripening stages. Kernel oil accumulation showed similar sigmoid patterns. Amygdalin and prunasin levels were undetectable in the sweet kernel cultivars throughout kernel development. During the early stages of apricot fruit development (before 50 DAF), the prunasin level in bitter kernels first increased, then decreased markedly; while the amygdalin level was present in quite small amounts and significantly lower than the prunasin level. From 50 to 70 DAF, prunasin further declined to zero; while amygdalin increased linearly and was significantly higher than the prunasin level, then decreased or increased slowly until full maturity. The cyanogenic glycoside accumulation pattern indicated a shift from a prunasin-dominated to an amygdalin-dominated state during bitter apricot kernel development and ripening. β-glucosidase catabolic enzyme activity was high during kernel development and ripening in all tested apricot cultivars, indicating that β-glucosidase was not important for amygdalin accumulation. Correlation analysis showed a positive correlation of kernel amygdalin content with fruit dimension parameters, kernel oil content and β-glucosidase activity, but no or a weak positive correlation with kernel dimension parameters. Principal component analysis (PCA) showed that the variance accumulation contribution rate of the first three principal components totaled 84.56%, and not only revealed differences in amygdalin and prunasin contents and β-glucosidase activity among cultivars, but also distinguished different developmental stages. The results can help us understand the metabolic mechanisms underlying differential cyanogenic glycoside accumulation in apricot kernels and provide a useful reference for breeding high- or low-amygdalin-content apricot cultivars and the agronomic management, intensive processing and exploitation of bitter apricot kernels.

Highlights

Apricot (Prunus armeniaca L.), which is an important Rosaceae family fruit crop, is a multipurpose tree species with ecological and economic value
We systematically analyzed the dynamic changes in amygdalin and prunasin accumulation, physical characteristics and chemical and biochemical parameters of ten apricot cultivars during fruit and kernel development and ripening
Correlation analysis and Principal component analysis (PCA) were performed to preliminarily explore the associations between cyanogenic glycoside accumulation and pomological traits linked to quality during fruit and kernel development

Summary

Introduction

Apricot (Prunus armeniaca L.), which is an important Rosaceae family fruit crop, is a multipurpose tree species with ecological and economic value. Amygdalin and its precursor prunasin are degraded by specific β-glucosidases, resulting in the release of toxic hydrogen cyanide, which serves as a defense mechanism against generalist herbivores [16] and imposes a large constraint on the use of apricot kernels to provide human or animal nutrition because of their bitter taste and toxicity. Long-term exposure to sublethal concentrations of cyanogenic glycosides can present ongoing health issues, such as Konzo, an irreversible motor neuron disease with clinical signs including the inability to walk, limited arm movement, and speech difficulties [29,30]. This poses an ongoing risk that needs to be managed to avoid future poisoning incidents. The use of apricot kernels for the development of drugs, food supplements, and functional foods may be of greater interest in markets where there are high-glycosides or non- or weakly cyanogenic varieties

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