Functional Properties of Yellowfin Tuna (Thunnus albacares) Skin Collagen Hydrolysate Fraction obtained by Ultrafiltration Purification

Hydrolyzed collagen with different fractions is broadly applied in various industries due to its functional properties. The study aimed to purify and fractionate the hydrolyzed collagen from yellowfin tuna skin by ultrafiltration and evaluate the functional properties of its fractions. The effect of temperature, pH, and pressure on membrane flux, nitrogen recovery efficiency, and degree of separation was investigated. Afterward, several functional properties of hydrolyzed collagen fractions including solubility, emulsification, foaming, and antioxidant properties were evaluated. The optimum ultrafiltration conditions for hydrolyzed collagen were temperature 25 °C, pH 6.5 and pressure 12 psi provided optimum membrane flux (3.4 L/m2.h) and nitrogen recovery efficiency (80.81%), and the smallest degree of separation (27.45%). The products after ultrafiltration were separated into two fractions, F1 (< 3 kDa), and F2 (3-5 kDa), with the volume of 10% and 90%, respectively. Both hydrolyzed collagen fractions were more than 96% soluble at pH below 8.0, where the F2 fraction dissolved better than F1. As pH was higher than 8.0, both fractions were almost completely dissolved. In addition, the emulsifying and foaming abilities of the F1 fraction were better than the F2. However, the F2 fraction was more resistant to oxidation with higher antioxidant activity. In conclusion, this research indicates that different fractions from hydrolyzed collagen from yellowfin tuna skin have various functional properties that could be applied in food, cosmetic and pharmaceutical industries.

Controlled-release N fertilizer to mitigate ammonia volatilization from double-cropping rice

Controlled-release nitrogen fertilizer (CRNF) can effectively enhance crop yields and raise the efficiency of nitrogen fertilizer in agroecosystems. In the present study, the volatilization of NH3 was determined by airflow enclosure chamber technique after the application of different CRNF rates in double-cropping rice fields in southern China for continuous 3 years. The early and late season rice (ESR and LSR) were cultivated each year. The results showed that the total NH3 volatilization losses ranged from 25 to 56 kg N ha−1 in ESR and from 32 to 61 kg N ha−1 in LSR. The loss of N to the total applied N ranged from 12 to 29% in ESR and from 12 to 27% in LSR. The application of CRNF significantly reduced the cumulative NH3 volatilization losses by 20–43% for ESR and by 20–32% for LSR compared with conventional urea application. CRNF in LSR was less effective to reduce NH3 volatilization than that in ESR. Furthermore, the application of 80% of N rate in the form of CRNF gave higher grain yield and apparent nitrogen recovery efficiency (ANRE) than that of application of 100% of N rate from conventional urea. CRNF can effectively reduce NH3 volatilization, and increase rice yield and ANRE. Considering higher price of CRNF, the application of CRNF at lower (20% applied N) rate than conventional urea in LSR may be a reasonable fertilization strategy for improving N use efficiency, environment effectiveness, and sustaining the development of rice production systems in double-cropping rice.

Optimal Nitrogen Practice in Winter Wheat-Summer Maize Rotation Affecting the Fates of 15N-Labeled Fertilizer

Lower nitrogen recovery efficiency (NRE) and negative environmental impacts caused by excessive nitrogen (N) fertilization threaten the sustainability of agriculture. Efficient and appropriate fertilization practices are extremely important to achieve higher crop yield with minimum N loss. A field microplot experiment was conducted in a wheat-maize rotation system in Shaanxi province, at North China Plain, using the 15N isotope tracer technique to qualify the different annual N managements in terms of crop yield, NRE, N distribution in plant-soil, and N losses to optimize the N management. The experiment included four N treatments: conventional practice with 510 kg ha−1 annually in four applications (N1), and three optimized N treatments, reducing N rate to 420 kg ha−1, adjusting topdressing fertilizer times and using slow-release fertilizer (SRF) (N2, N3, N4). The results showed that the grain yield and N uptake did not differ significantly among treatments. N from fertilizer taken up (Ndff) by wheat was not affected by N management; however, in maize, Ndff performed differently. Optimized treatments significantly decreased the Ndff as compared to N1 treatment. Furthermore, NRE of wheat and annual nitrogen recovery efficiency (annual NRE) did not differ among treatments in 2016 but significantly increased in 2017 compared to N1. Annual NRE in 2017 was similar to that obtained for wheat. For maize, optimized N managements decreased the NRE in N3 and N4 treatments of two years. Potential losses in wheat were also similar amongst treatments, but in maize, N3 and N4 had lower residual N in the soil’s top 60 cm but resulted in higher potential losses than N1 and N2. Overall, our results demonstrate that applying 420 kg N ha−1 annually in three applications and combining SRF and urea are effective to sustain crop yield, improve the efficiency of N usage by maize, and reduce N losses in this region.