Effect of proanthocyanidin‐rich extracts from Chinese quince ( Chaenomeles sinensis ) fruit on the physical and oxidative stability of sunflower oil‐in‐water emulsions

Acid-hydrolyzed phenolic extract of parsley (Petroselinum crispum L.) leaves inhibits lipid oxidation in soybean oil-in-water emulsions

The antioxidant activity of the natural phenolic extracts is limited in particular food systems due to the existence of phenolic compounds in glycoside form. Acid hydrolysis post-treatment could be a tool to convert the glycosidic polyphenols in the extracts to aglycones. Therefore, this research investigated the effects of an acid hydrolysis post-treatment on the composition and antioxidant activity of parsley extracts obtained by an ultrasound-assisted extraction method to delay lipid oxidation in a real food system (i.e., soybean oil-in-water emulsion). Acid hydrolysis conditions were varied to maximize total phenolic content (TPC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. When extracts were exposed to 0.6 M HCl for 2 h at 80 ℃, TPC was 716.92 ± 24.43 µmol gallic acid equivalent (GAE)/L, and DPPH radical scavenging activity was 66.89 ± 1.63 %. Not only did acid hydrolysis increase the concentrations of individual polyphenols, but it also resulted in the release of new phenolics such as myricetin and gallic acid. The extract's metal chelating and ferric-reducing activity increased significantly after acid hydrolysis. In soybean oil-in-water emulsion containing a TPC of 400 µmol GAE/L, the acid-hydrolyzed extract had an 11-day lag phase for headspace hexanal compared to the 6-day lag phase of unhydrolyzed extract. The findings indicated that the conversion of glycosidic polyphenols to aglycones in phenolic extracts can help extend the shelf-life of emulsion-based foods.

Modified Chinese quince oligomeric proanthocyanidin protects deep-frying oil quality by inhibiting oxidation

Chinese quince (Chaenomeles sinensis) fruit is an underutilized resource, rich in proanthocyanidins with antioxidant ability but poor lipid solubility. In this study, a novel modified oligomeric proanthocyanidin (MOPA) was prepared, which exhibited favorable lipid solubility (354.52 mg/100 g). It showed higher radical scavenging abilities than commercial antioxidant-BHA (butylated hydroxyanisole), both at 0.4-0.5 mg/mL. The addition of MOPA (0.04 %wt.) significantly increased the oxidative stability index of the soybean oil from 5.52 to 8.03 h, which was slightly lower than that of BHA (8.35 h). Analysis of the physicochemical properties and composition of oil during deep-frying showed that MOPA demonstrated significant antioxidant effects and effectively restricted the oil oxidation. This inhibition also delays the formation of heterocyclic amines (HAs) in fried food, thereby reducing the migration of HAs from food to deep-frying oil. Therefore, MOPA is a promising novel liposoluble antioxidant for protecting the quality of deep-frying oil.

Effect of Chinese quince proanthocyanidins on the inhibition of heterocyclic amines and quality of fried chicken meatballs and tofu

Heterocyclic amines (HCAs) have potential carcinogenic and mutagenic activity and are generated in cooked protein-rich foods. Adding proanthocyanidins (PAs) to these foods before frying is an effective way to reduce HCAs. In this study, polymeric PAs (PPA) and ultrasound-assisted acid-catalyzed/catechin nucleophilic depolymerized PAs (UAPA, a type of oligomeric PA) were prepared from Chinese quince fruits (CQF). Different levels of PPA and UAPA (0.05%, 0.1%, and 0.15%) were added to chicken meatballs and tofu; then these foods were fried, and the content of HCAs in them after frying was investigated. The results showed that PPA and, particularly, UAPA significantly inhibited the formation of HCAs in fried meatballs and tofu, and this inhibition was dose-dependent. The inhibition of HCAs by both PPA and UAPA was stronger in the chicken meatballs than in fried tofu. The level of total HCAs was significantly reduced by 57.84% (from 11.93 to 5.03 ng/g) after treatment of meatballs with 0.15% UAPA, with inhibition rates of 78.94%, 50.37%, and 17.81% for norharman, harman, and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), respectively. Of note, there was a negative correlation between water, lipid, protein, creatine, and glucose content and HCA content in the crust, interior, and whole (crust-plus-interior) measurements of all fried samples. Interestingly, PPA and UAPA were found more effective in inhibiting HCAs in the exterior crust than in the interior of the fried chicken meatballs. These results provide evidence that further studies on the reduction of the formation of harmful HCAs in fried foods by adding CQF PAs could be valuable to the fried food industry. PRACTICAL APPLICATION: Chinese quince proanthocyanidins treatments significantly inhibited the generation of heterocyclic amines (HCAs) in chicken meatballs and tofu when deep-fried. These results suggest that Chinese quince proanthocyanidins can be used as natural food additive for reducing HCAs in fried foods, laying the foundation for using Chinese quince fruit proanthocyanidins for HCA inhibition in the food industry.

Structural characterization of lignin-carbohydrate complexes from Chinese quince fruits extracted after enzymatic hydrolysis pretreatment

Chinese quince fruit (CQF) contains abundant pectin; however, the pectin cannot be efficiently separated by conventional approaches because of strong lignin-carbohydrate complexes (LCC). In this study, to elucidate the structural characteristics of the original LCC formed by lignin and pectin in CQF, single and multiple enzymatic hydrolysis pretreatments were innovatively performed, and the resulting LCC preparations were comprehensively characterized using a series of techniques. The enzymatic hydrolysis pretreatments significantly increase the LCC yield, releasing LCC fractions with low molecular weights (Mw = 4660-8288 Da). LCC-4, isolated by pretreatment with cellulase plus xylanase, had the highest galacturonic acid content (15.5 %), followed by LCC-2 (isolated by xylanase pretreatment) of 14.0 %. In CQF, lignin develops lignin-carbohydrate (LC) bonds with pectin to form LCC, with phenyl-glycoside bond being the dominant linkage. Although the pectinase pretreatment reduced the pectin content, signals of the LC linkages in the 2D-HSQC spectra were enhanced. LCC-4 could be considered as the most representative of the original LCC in CQF due to its high pectin content and multiple LCC signals in the 2D-HSQC spectrum. The structural understanding of the original LCC in CQF will lay a foundation for designing appropriate methods for extracting pectin from CQF.

Interaction between Chinese quince fruit proanthocyanidins and bovine serum albumin: Antioxidant activity, thermal stability and heterocyclic amine inhibition

Heterocyclic amines (HCAs) are carcinogenic and mutagenic substances produced in fried meat. Adding natural antioxidants (e.g., proanthocyanidins (PAs)) is a common method to reduce HCAs; however, the interaction between the PAs and protein can affect the inhibitory efficacy of PAs on the formation of HCAs. In this study, two PAs (F1 and F2) with different degrees of polymerization (DP) were extracted from Chinese quince fruits. These were combined with bovine serum albumin (BSA). The thermal stability, antioxidant capacity and HCAs inhibition of all four (F1, F2, F1-BSA, F2-BSA) were compared. The results showed that F1 and F2 interact with BSA to form complexes. Circular dichroism spectra indicate that complexes had fewer α-helices and more β-sheets, β-turns and random coils than BSA. Molecular docking studies indicated that hydrogen bonds and hydrophobic interactions are the forces holding the complexes together. The thermal stabilities of F1 and, particularly, F2 were stronger than those of F1-BSA and F2-BSA. Interestingly, F1-BSA and F2-BSA showed increased antioxidant activity with increasing temperature. F1-BSA's and F2-BSA's HCAs inhibition was stronger than F1 and F2, reaching 72.06 % and 76.3 %, respectively, for norharman. This suggests that PAs can be used as natural antioxidants for reducing the HCAs in fried foods.