Salted jellyfish by-products have collagen protein that is mainly sold for animal feed at a low price. The change of jellyfish by-products into a food ingredient like gelatine could benefit food applications and reduce food waste. Indeed, jellyfish gelatine production is a time-consuming process that includes alkaline pre-treatment, acid pre-treatment, hot water extraction, and drying. Reduced times of acid pre-treatment and water extraction might deliver different gel properties. Therefore, this research aimed to investigate the effect of hydrochloric acid (HCl) pre-treatment on the gel quality of resultant gelatine. Desalted jellyfish by-products were immersed in 0.5 M sodium hydroxide at 4oC for 1 h and then were acidtreated by varying HCl concentrations (0.1, 0.2, and 0.3 M) at 25oC for 2 h. After that, samples were extracted at 60oC for 3 h and dried at 60oC for 3 days. Results showed that gelatine yield significantly increased with increasing HCl concentration. Gelatine yield were 2.97±0.97%, 5.60±1.01%, and 6.34±1.08%, after extraction with 0.1, 0.2, and 0.3 M HCl, respectively. Gel strength generally decreased as HCl concentration increased. Gel strength values were in the range of 118.89-223.60 g. The colour of jellyfish gelatine showed light to dark brown with no differences in Hue values. Thus, the short duration of HCl pre-treatment for 2 h and hot water extraction for 3 h was insufficient for the jellyfish gelatine process.

Edible jellyfish have been consumed as food for more than a century with offering high protein and crunchy texture. The pepsin hydrolysis of jellyfish protein yields jellyfish protein hydrolysate (ep-JPH), reported for potential bioactivities such as antioxidant activity or antihypertensive activities. Due to the substantial number of by-products generated from jellyfish processing, the by-products were then selected as a raw material of JPH production. This research aimed to evaluate the effect of the hydrolysis time of pepsin on the antioxidant activity of ep-JPH. The dried desalted jellyfish by-products powder was enzymatically hydrolysed by 5% (w/w) pepsin, and the hydrolysis time was varied from 6, 12, 18, and 24 h at 37oC. Results showed that increased hydrolysis time increased the degree of hydrolysis (DH) and inhibition of DPPH radical. The 24 h ep-JPH possessed the highest DH and the highest inhibitory effect of DPPH radical. The results demonstrated that, in this experiment, all ep-JPHs were DPPH radical scavengers, exhibiting different inhibition activities depending on DH values.

Protein hydrolysates are products of protein degradation that provide various sizes of peptides and free amino acids. Protein hydrolysate from the different types of enzymes and raw materials provides different bioactivity, such as antioxidant and antibacterial activity. Salted jellyfish by-products have the potential to be a source for protein hydrolysate production because of their low price and having collagen protein. This research aimed to evaluate the antioxidant and antibacterial activity of protein hydrolysates from jellyfish by-products. The dried salted jellyfish by-products from the umbrella and oral arm part of white-type (Lobonema smithii) and sand-type (Rhopilema hispidum) were desalted and enzymatically hydrolyzed by 5% (w/w) pepsin for 24 h at 37°C. Bioactivity assays showed that the hydrolysate of the oral arms part of white-type jellyfish exhibited the highest antioxidant activity (13.27%). While protein hydrolysate of umbrella part of sand-type jellyfish showed the highest antibacterial activity against Vibrio parahaemolyticus up to 13.61%. The results demonstrated that peptic hydrolysate of different types and parts of jellyfish by-products provided different antioxidant or antibacterial activity, thereby increasing the potential uses of jellyfish protein hydrolysate as a functional food.

By-products of the marine industry have gained attention for producing valuable food ingredients like gelatin, which might benefit food applications and decrease food waste. Gelatin is the only protein-based food hydrocolloid, mainly used for gelling, viscosity, or emulsifying in the food industry. So far, a number of researchers have reported that by-products of salted jellyfish can produce jellyfish gelatin. The quality of jellyfish gelatin gel depends on several factors including hydrochloric acid pretreatment, extraction temperature, and extraction time. However, the functional properties such as foaming and emulsifying of jellyfish gelatin are not well understood. This research was aimed at investigating the hydrochloric acid pretreatment effect of extraction times (12, 24, and 48 h) at 60 °C on the resulting gelatin's yield, physical, and functional properties. Results showed that jellyfish gelatin's yield, gel strength, and viscosity significantly increased with increasing extraction times. Jellyfish gelatin yields were 2.74-14.07%. The gel strength of jellyfish gelatin extracted for 48 h (325.97±2.84 g) was higher than that of jellyfish gelatins extracted for 12 h (210.46±3.97 g) and 24 h (261.60±3.25 g). All jellyfish gelatins can form gels at 4 °C. Viscosity values of jellyfish gelatin were 23.00-24.50 centipoise. The foaming capacity and foaming stability of jellyfish gelatin were 12.28-17.54% and 10.52-15.78%, respectively. The emulsification activity index of jellyfish gelatin was 13.11-13.30 m2/g, and the emulsification stability index was 39.19-56.42%. As a result, varied gelatin extraction periods influenced jellyfish gelatin's physical and functional properties, indicating that the extended extraction time of 48 h delivered the jellyfish gelatin that can be used as a foaming and emulsifying agent. Therefore, turning the jellyfish by-products into food ingredients like gelatin would increase product values and potential uses in the food and medical applications.