Peng Han

PulY103B was immobilized onto magnetic chitosan/Fe₃O₄ nanoparticles, achieving an activity recovery of 65.3%. The optimal reaction conditions and stability of the immobilized enzyme were similar to those of the free enzyme. Based on its substrate specificity, the immobilized PulY103B was identified as a type II pullulanase. Although its behavior differed from that of the free enzyme, it retained 4-α-glycosyltransferase activity. Following combined treatment with immobilized PulY103B (at 35 °C, pH 6.5) and autoclaving, the resistant starch (RS) content of potato starch increased from 7.9% in the raw material to 47.2%. X-ray diffraction (XRD) patterns revealed that the treated starch not only retained the original B-type diffraction peaks but also exhibited a characteristic V-type crystalline peak at 20°, indicating that the resulting product could be classified as RS type III+V (RS III+V). The operational stability of the immobilized PulY103B was evaluated during the preparation of potato RS. After five consecutive reaction cycles, the immobilized enzyme retained 50.2% of its initial activity. These findings demonstrate that immobilized PulY103B has considerable potential for the continuous production of potato RS III+V under mild conditions.

This study investigated the use of exogenous lipase and protease to produce dry‐cured meat with ham‐like flavor. The results showed that the best formula was injection of 11.5 × 10 ³ U/kg protease and 6.0 × 10 ³ U/kg lipase after salting and holding for 110 days. The best product has similar color ( L ^∗ , 42.0; a ^∗ , 11.3; b ^∗ , 11.2), proteolysis index (PI) (28.7%), and thiobarbituric acid reactive substances (TBARSs) (1.17 mg MA/kg) with Xuanwei ham from the Xuanwei local market ( p > 0.05), and lower values of total volatile basic nitrogen (TVB‐N) (49.9 mg/100 g) compared to the Xuanwei hams ( p < 0.05). Moreover, the best product contained higher levels of specific key flavor compounds compared to the Xuanwei hams, and its most abundant volatile compounds (hexanal, amyl alcohol, hexanol, and 2‐heptanone) had similar rates (2.7:1:2.6:10.4) to the Xuanwei ham from the Xuanwei local market (3.2:1:2.8:9.4). Furthermore, the best product has similar values of total free amino acids (FAAs) (103.2 mg/100 g) and bitter amino acids (45.6 mg/100 g) to the Xuanwei hams, and its values of sweet amino acids and umami amino acids were similar to Xuanwei hams from the Xuanwei local market and Teh‐Ho Canned Food Company, respectively ( p > 0.05). It demonstrated that the addition of exogenous enzymes was an effective way of producing dry‐cured meat with ham‐like flavor in a relatively short period.

The potential of PulY103A (a moderate amylopullulanase originating from Bacillus megaterium) for resistant starch production under moderate conditions (40 °C; a pH of 6.5) was investigated. PulY103A was much more suitable for pea resistant starch production with a high growth rate of 3.63. The pea resistant starch (PSpa) produced with PulY103A had lower levels of swelling power and solubility and a better level of thermostability than native pea starch (PSn) and autoclaved PS (PSa). The starch crystallinity pattern was B + V, which indicated that the PSpa belonged to RS types III + V. In addition, PSpa was used for breadmaking. The results showed that the bread quality was not significantly influenced compared to the control group when the content of PSpa was under 10% (p > 0.05). The bread supplemented with 10% PSpa had a significantly increased TDF content compared to that of the control (p < 0.05). Moreover, the in vitro mineral bioavailability of the bread sample was influenced gently compared to other dietary fibers, and the bread sample changed from a high-glycemic-index (GI) food to a medium-GI food corresponding to white bread at the same concentration of PSpa. These results indicated that PSpa is a good candidate for the production of dietary foods.

This study aims to find a moderate pullulanase for detergent industry. The pulY103B gene (2217 bp) from Bacillus megaterium Y103 was cloned and expressed in Escherichia coli. PulY103B contained four conserved regions of glycoside hydrolase family (GH) 13 and the typical sequence of type I pullulanase. The optimal reaction conditions of PulY103B were pH 6.5 and 40 °C. In addition, it remained stable below 40 °C and over 80% of activity was retained at pH ranging from 6.0 to 8.5. The best substrate for the enzyme was pullulan. Furthermore, it exhibited activity toward wheat starch (36.5%) and soluble starch (33.4%) but had no activity toward amylose and glycogen. Maltotriose and maltohexaose were major pullulan hydrolysis products. Soluble starch and amylopectin were mainly hydrolyzed into maltotetraose. These results indicated that PulY103B is a novel type I pullulanase with transglycosylation activity via formation of α-1,4-glucosidic linkages. Moreover, PulY103B was strongly stimulated by nonionic detergents [viz, Tween 20 (10%), Tween 80 (1%), Triton X-100 (20%)] and commercial liquid detergents (3.0 g/L). Wash performance tests demonstrated that the mixture of PulY103B and detergent removed starch-based stains better than using detergent alone (p < 0.05). Therefore, this pullulanase has big potential as a detergent additive.

The effects of edible coatings based on sodium alginate with ʻBaozhuʼ pear chitinase on the quality of cherry tomatoes during refrigerated storage were evaluated. Cherry tomatoes inoculated with Fusarium oxysporum were coated and stored up to 21 days. All coatings with the chitinase significantly reduced F. oxysporum proliferation on cherry tomatoes during storage and extended the shelf life of cherry tomatoes effectively (p < .05). Results showed that alginate coatings with the chitinase could prevent weight loss, maintain firmness, and slow down the changes of titratable acidity and vitamin C (p < .05) in a dose‐dependent manner. However, no significant differences were observed between T3 (1% alginate/0.15% ʻBaozhuʼ pear chitinase/1% glycerin) and T4 (1% sodium alginate/0.3% ʻBaozhuʼ pear chitinase/1% glycerin) (p > .05). Overall, alginate coating with 0.15% ʻBaozhuʼ pear chitinase could be a promising method to maintain the quality of cherry tomatoes.

Summary: Heat treatment will affect the nutritional properties and potential bioactivity of food materials. The aim of this work was to evaluate the effect of different thermal treatment (4, 56, 65 and 100 ℃) and in vitro gastrointestinal digestion on the antioxidant activity of egg white hydrolysate. The results demonstrated that egg white hydrolysate treated at 65 ℃ exhibited the highest antioxidant. Remarkably, the simulated digestion significantly increased antioxidant activity of egg white hydrolysate. Furthermore, we identified twenty‐four potential antioxidant peptides by performing mass spectrometry and bioinformatic analysis. Six peptides were selected based on the activity prediction score of the online tool. The results showed that P6 (ACPECPK) possessed the most outstanding antioxidant properties and had low cytotoxicity and allergenicity. Bioinformatics technology combined with biochemical assays may offer a way for discovering novel antioxidant peptides from different kinds of food under various heat treatment conditions.

Summary: A strain, Rahnella aquatilis L103, which was isolated from the soil around the roots of mushrooms, produced antibacterial protein though fermentation. This protein has broad antibacterial spectrum towards gram‐positive and gram‐negative bacteria. The protein has a significant antioxidant capacity on scavenging ABTS^+· (82.5%, 120 μg mL⁻¹), DPPH^· (64.1%, 600 μg mL⁻¹) and OH^· (60.1%, 750 μg mL⁻¹) as well. The protein was considered to be safe within concentration of 150 μg mL⁻¹ as shown by MTT results and was applied to beef refrigerated preservation. The treatment group presented lower total viable counts (TVC), total volatile basic nitrogen (TVB‐N), 2‐thiobarbituric acid (TBA), meanwhile, higher sensory score and longer shelf life (2 days) compared with the control group (P < 0.05). The results indicated that the protein under safe concentration was beneficial to beef preservation.