Abstract Agar is a strongly gelling polysaccharide extracted from gracilarioids, which is processed through conventional alkaline pre-treatment and chemical bleaching. However, the use of chemical bleaching agents has associated health risks to humans and the environment. The aim of the present study was to determine the effects of photo-bleaching in combination with NaOH pre-treatments at 5, 10 and 15% concentrations on the physico-chemical properties of agar extracted from Gracilariopsis heteroclada. The results highlighted that the gel strength of photo-bleached agar extracts PBA-15 (1822.00 g cm−2), PBA-10 (1465.60 g cm−2), and PBA-5 (1067.70 g cm−2) were significantly higher than in either a commercially sourced agar reference sample (756.20 g cm−2) or a chemically bleached agar (390.94 g cm−2). The physico-chemical properties of PBA extracts fell within the acceptable limits of food-grade agar. Photo-bleached agar extracts (PBA-5, PBA-10, PBA-15) also exhibited a higher lightness (L*) and whiteness index (WI) which makes these agars ideal for microbiological use. This study demonstrated that photo-bleaching by solar irradiation improved the physico-chemical properties of agar from G. heteroclada without the use of a chemical bleaching agent.

中文翻译：

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异枝芽孢杆菌光漂白琼脂提取物

摘要 琼脂是从短纤蕈类中提取的一种强胶凝多糖，经常规碱预处理和化学漂白加工而成。然而，化学漂白剂的使用会对人类和环境带来健康风险。本研究的目的是确定光漂白与 5%、10% 和 15% 浓度的 NaOH 预处理相结合对从异枝芽孢杆菌中提取的琼脂的理化性质的影响。结果强调，光漂白琼脂提取物 PBA-15 (1822.00 g cm-2)、PBA-10 (1465.60 g cm-2) 和 PBA-5 (1067.70 g cm-2) 的凝胶强度显着高于在商业来源的琼脂参考样品 (756.20 g cm-2) 或化学漂白琼脂 (390.94 g cm-2) 中。PBA 提取物的理化性质在食品级琼脂可接受的范围内。光漂白琼脂提取物（PBA-5、PBA-10、PBA-15）还表现出更高的亮度 (L*) 和白度指数 (WI)，这使得这些琼脂成为微生物学应用的理想选择。这项研究表明，在不使用化学漂白剂的情况下，通过太阳辐射进行的光漂白改善了异枝菌琼脂的理化性质。