Effect Of Acetic Acid Treatment On Thermal Processing Quality And Cell Wall Polysaccharide Structure Of Arrowhead Slices

Arrowhead is widely consumed as an aquatic vegetable with high nutritional value.Thermal processing is often performed to remove the bitterness of raw arrowhead,but the operation can lead to softening of the texture of arrowhead,making the final texture unsatisfactory for many consumers.Acetic acid as a common food additive,can effectively alleviate the softening of thermal processed fruit and vegetable.Furthermore,acetic acid is the most effective compared to other organic acids.Currently,there are no studies on the application of acetic acid to the texture regulation of arrowhead.In this study,firstly,the effects of acetic acid pretreatment on the quality of arrowhead such as texture,color,total phenolic content,digestive characteristics,and flavor were investigated.Followed by the mechanism of acetic acid pretreatment to alleviate the softening of texture in thermal processing.Finally the results were further validated by ball milling and enzymatic degradation.The main findings were as follows:1.Effect of acetic acid pretreatment on the edible quality of arrowhead bulbs.Some of the arrowhead bulb slices was immersed in 0.6%acetic acid for 15 h（AAI）and another immersed in distilled water for 15 h（DWI）as a control,then cooked in boiling water for 30 min（AAIC,DWIC）to study the effect of different treatment on the quality of arrowhead bulb slices.The results showed that the hardness of arrowhead bulb slices effectively alleviated the softening and made arrowhead bulb slices have white color and maintained the total phenol content by acetic acid treatment.The glucose content of the samples in AAIC group was lower than that of DWIC group after digestion in viro,which indicated that acetic acid treatment could reduce the digestibility of the arrowhead.The results of electronic nose and gas chromatography-mass spectrometry showed that there were some differences in the flavor of the different treatment groups.The volatile substances of arrowhead bulb slices were mainly composed of cyclohexanal,nonaldehyde,decaldehyde,linalool,2-n-pentyl furan,D-limonene and other substances.The volatile substances of arrowhead bulb slices treated with acetic acid were more than those treated with distilled water before or after cooking.2.Effect of acetic acid pretreatment on the cell wall and cell wall polysaccharide of arrowhead bulbs.To investigate the relationship between the change of texture and cell wall and cell wall polysaccharides of arrowhead bulb.The changes of cell wall of arrowhead bulb slices from different treatment groups were observed by SEM.The in situ observation of pectin was achieved by in situ labeling with different monoclonal antibodies.The changes of atoms or functional groups in cell wall were determined by FT-IR.Next,the cell wall fractions were extracted sequentially,the monosaccharide composition,sugar ratio,molecular weight and thermal properties of each fractions were analysed.The results showed that the integrity of cell wall structure was effectively maintained during thermal processing after acetic acid pretreatment,however,the cell wall was damaged seriously after distilled water pretreatment.The fluorescence intensity of LM20 antibody labeling in AAIC group was higher than that in DWIC group,but the fluorescence intensity of LM6-M and LM26 antibody labeling was lower than that in DWIC group.In the infrared spectrogram,the intensity of the peak at 1650 cm^-1which is associated with the carboxyl group,was increased in DWIC and AAIC samples compared with DWI and AAI,while the peak at 1110 cm^-1was decreased,which is associated with the typical absorption band of polygalacturonic acid.The GalA content increased in the WSF of DWIC group during thermal processing,the Ara and Gal content increased in the WSF of AAIC group,and the pectin characteristic sugars were also found in the HF.The polymer concentration and molecular weight distribution pattern of AAIC and DWIC were pronounced changed,the peak time shifted to the right and the concentration of small molecular weight substance in AAIC was increased compared with AAI and DWI.3.Further investigation of the effect of acetic acid pretreatment on cell wall polysaccharides by ball milling and enzymatic degradation.To further investigate the effect of acetic acid pretreatment on cell wall polysaccharides,pectin and（hemi-）cellulose action sites were gradually destroyed by ball milling at different times.The specific action sites were degraded by arabinoglucanase and galactanase enzymes,and then the degraded fractions were analysed by extraction rate,FT-IR,monosaccharide composition,sugar radio,X-ray,thermal characterization,molecular weight determination and SEM.The results showed that the particles size of the residue were reduced,the enzymatic sites were increased and the crystallization type was changed by ball milling.Arrowhead polysaccharides contained more arabincan side chains than galactan side chains.The RG-Ⅰside chain of arrowhead polysaccharides contains AGⅠtype side chains and there is mainly interaction between AGⅠtype side chains and（hemi-）cellulose.A comprehensive analysis of thermal analysis,molecular weight,SEM images and monosaccharide data showed that acetic acid treatment changed the distribution state of pectin and（hemi-）cellulose to be more uniformly distributed and more tightly bound compared with the distilled water treatment group,but the DNUSF group was present through pectin wrapped cellulose.