The effects of fermentation by cholesterol-lowering fungi on the functional components and bioactive properties of kiwifruit pomace

Kiwifruit pomace, a processing byproduct with lipid metabolism-regulating potential, is often discarded because of its low bioavailability. In this study, fungal fermentation, which is an efficient bioprocessing strategy, was applied to increase the contents of its active components and its bioavailability. Seven cholesterol-lowering fungal strains isolated from fermented foods—Talaromyces sp. FR, Aspergillus sp. C1YC, Fusarium solani A4YC, Alternaria alstroemeriae C2SLB, Monascus purpureus HQM, Penicillium rubens C3SLB, and Penicillium chrysogenum C2YC—were used for pomace fermentation. The contents of flavonoids, total phenolics, and soluble dietary fibre significantly increased (P < 0.05), with the greatest increases (1.94-, 1.42-, and 1.31-fold, respectively) observed in the HQM group. All the strains and fermented pomace extracts exhibited considerable cholesterol-degrading ability, reaching 74.79 % with the HQM suspension. Extracts of C1YC and C3SLB showed prominent antioxidant capacity, whereas the HQM extract strongly bound bile salts. α-Glucosidase activity and α-amylase activity were inhibited by the C2YC and HQM suspensions (84.84 % and 83.01 %, respectively). Compared with the control, the FR-fermented pomace adsorbed 6.01 times more fat. This study is the first to report direct cholesterol degradation by Talaromyces sp., Fusarium solani, and Alternaria alstroemeriae, confirming that fungal fermentation increases the value of kiwifruit pomace.

Hypercholesterolemia is recognized as a significant risk factor for atherosclerotic cardiovascular disease (ASCVD), posing a major public health challenge worldwide. Kiwifruit, regarded as a nutrient-dense fruit, is rich in high-quality dietary fibre and contains substantial amounts of polyphenols and flavonoids, which exhibit notable antioxidant activity. These bioactive compounds have been demonstrated to regulate physiological functions, prevent chronic diseases, and beneficially alter blood lipid profiles. With the rapid expansion of the global kiwifruit industry and increasing consumer demand, the market for fresh fruits and processed products—such as juice and dried fruit—has continued to grow. Consequently, significant quantities of byproducts, primarily composed of peel, seeds, and residual pulp, are generated during processing. This biomass, which is abundant in dietary fibre, polyphenols, and flavonoids, is currently underutilized and often discarded as waste. Such practices not only result in the loss of valuable bioactive components but also contribute to solid waste accumulation and environmental risks, thereby hindering the sustainable development of the kiwifruit industry.

As one of the most species-rich and biologically diverse groups on Earth, fungi are recognized as significant reservoirs for the discovery of bioactive metabolites. Previous studies have demonstrated that fungi isolated from various sources exhibit considerable potential for reducing cholesterol levels and alleviating obesity-induced hyperglycaemia. For instance, crude extracts derived from mangrove-associated Talaromyces sp., the endophytic fungus Aspergillus sp. obtained from Eucommia ulmoides leaves, Alternaria destruens (AKL-3) isolated from Calotropis gigantea, and Penicillium canescens sourced from juniper berry pulp have been reported to display multiple biological activities, including antioxidant, α-glucosidase inhibitory, and antimicrobial effects. Moreover, metabolites produced by Monascus species have been confirmed to possess notable lipid-lowering, hypoglycaemic, and antihypertensive properties. Collectively, these findings indicate that fungi represent a highly promising resource for the development of functional metabolites.

Fungal fermentation has been recognized as an effective strategy for enhancing the quality of plant-based foods. Through microbial metabolism, macromolecules such as polysaccharides and proteins in plant substrates are broken down into smaller, more readily absorbable molecules, thereby enabling the release and enrichment of bioactive compounds. In recent years, numerous studies have focused on the application of fungal fermentation for the development of foods or ingredients with improved functional properties. For example, kochujang fermented with Aspergillus oryzae has been demonstrated to exhibit significant cholesterol-lowering effects, while the fermentation process involving Monascus purpureus has been reported to partially remove cholesterol. In addition, citrus peel extract fermented with Aspergillus niger has shown potential for alleviating obesity and related hyperglycaemic symptoms.

With respect to the increase in antioxidant activity, solid-state fermentation using various fungi—such as Aspergillus niger, Rhizopus oligosporus, and Monascus spp.—on substrates such as apple pomace, oats, soybeans, guava leaves, and brown seaweed has been shown to significantly increase the contents of polyphenols and flavonoids, along with improving free radical scavenging capacity. It has also been reported that the fermentation of apple pomace by Aspergillus niger ZDM2 and Aspergillus tubingensis ZDM1 increased the antioxidant activity to three and five times that of unfermented samples, respectively. Similarly, the fermentation of dairy sludge by Monascus purpureus resulted in an approximately twofold increase in antioxidant activity . Moreover, the fermentation of tea with Monascus spp. is considered a promising approach for enhancing the effects of functional constituents and increasing product quality. These findings collectively indicate that fungal fermentation has broad application prospects in the development of functional plant-based foods.

Recent research on the fermentation of kiwifruit pomace predominantly focuses on lactic acid bacteria and yeasts. Examples include beverage preparation by Lactiplantibacillus plantarum fermentation, novel liquor development by yeast-based SSF, and bioethanol production using Saccharomyces bayanus, aimed at reducing waste and improving utilization. However, a significant research gap exists concerning the application of fungal fermentation technology to kiwifruit pomace, specifically for the development of functional products targeting hypercholesterolemia or obesity. Filling this gap by exploring the hypocholesterolaemic potential of kiwifruit pomace fermented with specific fungi and its application in functional foods represents a critical future research direction.

This study aims to explore fermentation strategies for increasing the utilization and value of kiwifruit pomace. By thoroughly analysing changes in functional properties and bioactivity during fungal fermentation, novel insights and technical support for the sustainable development of the kiwifruit industry and functional health food innovation can be achieved.