Abstract
Mulberry leaf is an excellent protein resource that can be used as feed additive for livestock and poultry. Nevertheless, the use of mulberry leaves in animal diets is limited by its protease inhibitors, tannic acid and other anti-nutritional factors. This study systematically analyzed the type and activity of serine protease inhibitors (SPIs) from the leaves of 34 mulberry varieties, aiming to reveal the physicochemical properties and inactivation mechanism of SPIs. The types and activities of trypsin inhibitors (TIs) and chymotrypsin inhibitors (CIs) exhibited polymorphisms among different mulberry varieties. The highest number of types of inhibitors was detected in Jinshi, with six TIs (TI-1~TI-6) and six CIs (CI-1~CI-6). TIs and CIs exhibited strong thermal and acid–base stability. High-temperature and high-pressure treatment could reduce the activities of TIs and CIs to a certain extent. β-mercaptoethanol treatment could completely abolish TIs and CIs, suggesting that the disulfide bridges were critical for their inhibitory activities. The Maillard reaction could effectively eliminate the inhibitory activities of TI-1~TI-4 and CI-1~CI-4. This study reveals the physicochemical properties and inactivation mechanisms of the anti-nutritional SPIs from mulberry leaves, which is helpful to exploit mulberry-leaf food with low-activity SPIs, promote the development and utilization of mulberry-leaf resources in animal feed and provide reference for mulberry breeding with different functions.
Highlights
Mulberry, belonging to the Moraceae family, is a deciduous tree or shrub
We speculate that some serine protease inhibitors (SPIs) from mulberry leaves may act as important anti-nutritional factors affecting protein digestion and absorption in animals
In order to explore whether anti-nutritional trypsin inhibitors (TIs) and chymotrypsin inhibitors (CIs) inhibitory activities were present in mulberry leaves, cultivated mulberry Guang1 was randomly selected as the research object
Summary
Mulberry, belonging to the Moraceae family, is a deciduous tree or shrub. China has the most abundant germplasm resources of mulberry in the world, with 15 species and 4 varieties. As the feed of pigs, sheep, chicken broilers and other livestock, mulberry leaves can improve the conversion efficiency of feed nutrition in animals and enhance the quality of livestock and poultry products [7–9]. We analyzed the types, activity polymorphisms and physicochemical properties of TIs, CIs, EIs and SIs from the leaves of 34 mulberry varieties and explored the inactivation mechanisms of TIs and CIs from mulberry leaves. Such knowledge would enhance the nutrient utilization of mulberry leaves, provide a theoretical basis and new approaches for the development of mulberry-leaf products with low-activity SPIs and promote the exploitation and utilization of mulberry-leaf resources in animal feed
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