The Phytochemical Properties of Low-Grade Longan Syrup and Its Potential Use as a Dietary Supplement for Honey Bees

Climate change significantly affects honey bee populations and their access to natural food sources, demanding alternative economic feed sources. Longan stands out as the most important fruit crop in Southeast Asia, but with a surplus of low-grade fruit that is not suitable for the market. This study investigates the potential of longan syrup as an alternative carbohydrate source for honey bees by measuring sugar composition, phytochemical profiles, feed, and survival, as well as the resulting gut microbial changes. Processed longan syrup contains 8.2, 85.1, and 33.1 mg/g of sucrose, glucose, and fructose. Total phenolic and flavonoid contents were 24.94 and 129.78 mg/g, respectively, showing a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition rate of 26.78% and an 87.82% antiradical activity rate via 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). In vitro supplementation studies indicated that survival was highest in the 50% <i>w</i>/<i>v</i> sucrose syrup condition (control), followed by honey bees fed with 10%, 20%, and 30% longan syrup concentrations, respectively. Analyses of honey bee gut microbiomes revealed that longan syrup supplementation increased fermentative microorganisms such as <i>Lactobacillus</i> and <i>Fructobacillus</i>, which are beneficial for honey bees' health. Even though the addition of higher amounts of longan syrup would not be recommended, a 10% addition would be beneficial to honey bees' health through the modulation of gut microbiomes, demonstrating its potential as a dietary supplement that is a cost-effective and sustainable alternative to sugar syrup during shortages of natural carbohydrate sources.