Optimization of parameters for enzymatic and bacterial hydrolysis of seaweeds and the effects of two products on the stress resistance of Chinese flowering cabbage

Objectives Seaweed is one of the marine resources; its hydrolyzed product has growth-promoting and stress resistance effects. Here we optimized the parameters of two routine seaweed processing and compared their products.

Methods Single factor and orthogonal experiments were used for the optimization of procession parameters for bacterial and enzymatic hydrolysis of brown algae (Laminaria japonica). In bacteria degradation and enzymatic hydrolysis process, the substrate concentration, algae dosage, pH value and temperature for the degradation were optimized, the used bacteria were Microbulbifer sp. SH-1 and alginate lyase AlgSH7. Meanwhile, the morphology of seaweed cells was observed before and after both kind of hydrolyzation under optical microscope. The effects of the two kinds of products were tested with a pot experiment, using Chinese cauliflower cabbage as test material.

Results The optimal conditions for alginate lyase AlgSH7 were 2% substrate concentration, 6% enzyme dosage, pH 8.5 and degradation temperature of 44℃. For strain SH-1, the optimal conditions were 2.5% substrate concentration, 1.5% bacterial solution, pH 7.5 and degradation temperature of 32℃. Compared with bacteria degraded product (BDP), the enzyme hydrolyzed products (EHP) increased alginate and total sugar contents and reduced sugar by 141.8%, 57.6%, and 150.5%, respectively. The contents of polyphenol, mannitol, and betaine decreased by 35.3%, 60.6%, 62.6%, respectively. The yield of BDP was 9.3% higher than that of the EHP. Before hydrolyzation, the kelp primitive cells were tightly arranged, and their traits were regular and full. With prolonged bacterial or enzymatic hydrolysis, the visible area of kelp cells became smaller, and the distance between cells increased. After being degraded by enzymatic hydrolysis for 24 h, the visible area of seaweed cells was only 77.2% of that by bacterial hydrolysis. Pot experiments showed that under moderate drought conditions (relative soil water content 50%), the crop biomass treated with EHP was 13.7% higher than that treated with BDP. The crop biomass treated with EHP and water-soluble fertilizer (NPK, N∶P₂O₅∶K₂O=110∶50∶60) was 10.6% higher than that treated with BDP and NPK. Under waterlogging stress conditions (2 cm depth of waterlogging layer), the crop biomass treated with EHP was 7.1% lower than BDP treated biomass but (P<0.05) was higher than that of the control. The biomass treated with EHP+NPK was 5.6% higher than that treated with BDP+NPK. Under salt stress (NaCl content in soil was 24 g/kg), the biomass of Chinese cabbage treated with EHP showed an increasing trend, but the increase was not significant compared with that treated with BDP.

Conclusions The algae products from enzymatic hydrolysis had higher contents of alginic acid, total sugar, reducing sugar, but lower contents of polyphenol, mannitol and betaine than the algae products from bacterial degradation. Although there was low algae yield from enzymatic hydrolysis, the ensuing product had higher growth-promoting, drought and waterlogging resistance ability, regardless of sole or combined fertilizer application.