Effects Of Acid And Alkali Treatment On Quality And Cell Wall Polysaccharide Of Thermal Processed Lotus Rhizomes Slices

The texture difference of lotus rhizome is the main reason that affects its processing mode and price,so it is very important to master the mechanism of texture difference after heat processing and achieve the desired taste through regulation.Acetic acid and sodium bicarbonate are two commonly used food additives,and they have been found to regulate texture in other fruits and vegetables.However,the application of acetic acid and sodium bicarbonate to the texture regulation of lotus rhizome is relatively rare.In this paper,the effects of acetic acid and sodium bicarbonate on the texture,color,nutrition,digestion and flavor of lotus rhizome were studied to determine the feasibility of acid and alkali treat-ment.Secondly,the effect of acid and alkali treatment on the cell wall was explored by selecting two kinds of lotus rhizomes(Lulinhu and Miancheng)with typical textures.The main findings are as follows:1. Effect of acid and alkali treatment on texture,color,nutrition,digestion and flavor of lotus rhizomeLotus rhizome was treated with 0.1%acetic acid(v/v)and 0.1%sodium bicarbonate(w/v)solution,and its hardness,color,total phenol,Vc,simulated digestion in vitro and volatile flavor compounds were determined.The results showed that acetic acid treatment could significantly improve the boiling hardness of lotus rhizome and keep its white color all the time.On the contrary,the hardness of lotus rhizome treated with sodium bicar-bonate decreased significantly,and the color was ruddy.The fresh sample have the high-est total phenol(about 1300μg/g)and Vc content(about 0.3 mg/g)but the content de-creased significantly after heat treatment.There was no significant difference between the other treatment groups except for the higher content of Vc in acetic acid treatment group(about 900μg/g).Sodium bicarbonate treatment can significantly change the digestion and absorption mode.Due to the pectin decomposition in the middle lamella,the cell structure of the softened lotus rhizome is relatively complete after a short period of ho-mogenization.The cell contents are not completely released,resulting in a low level of total carbohydrate in the gastric digestive fluid(about 300 g/L)while the distilled water treated group and acetic acid treated group have the high level(500 g/L).However,in the simulated intestinal digestion,the total carbohydrate content in the intestinal digestive fluid will still increase.The results of electronic nose and SPME-GC-MS showed that the main components of lotus flavor were dimethyl sulfur,n-octanal,nonanal,sunflower al-dehyde,etc.After the treatment of sodium bicarbonate,the amount of dimethyl sulfur and ester compounds in lotus rhizome increased.2. Effect of acid and alkali treatment on texture and cell wall polysaccharide of lotus rhi-zomeIn order to explore the relationship between the maintenance of lotus rhizome texture and cell wall polysaccharides,the structure of cell wall,the change of cell wall group,the content of polysaccharide in cell wall,the monosaccharide composition of polysaccharide,the sugar ratios and the degree of esterification of polysaccharide were analyzed.The re-sults showed that the integrity of cell wall was very important to the texture quality of lo-tus rhizome.Acetic acid treatment can maintain cell wall integrity,while sodium bicar-bonate treatment is the opposite.However,there were no significant differences in the cell wall except for pectin-related groups under different treatments,indicating that the cellu-lose-hemicellulose backbone of the cell wall was relatively stable before and after heating.Heating can reduce the esterifying degree of cell wall,while acid and alkali treatment can intensify the de-esterification reaction.The integrity of cell wall is closely related to the content of chelate-soluble fraction(CSF),and the main effect of acid and alkali treatment on the texture of lotus rhizome is the decreased content of CSF after heat treatment.For fresh sample,the content of CSF and homogalacturonan is higher,while Miancheng has more side chain structure.Heat treatment had a great influence on the backbone of lotus rhizome in Lulinhu,but had a great influence on the side chain of Miancheng.3. Purification method and advanced structure of CSFThe key change sites of lotus rhizome cell wall during heat treatment were deter-mined by atomic force microscopy.The purification method of CSF from lotus rhizome was studied by column chromatography and ultrafiltration membrane purification.Mo-lecular weight was determined by gel chromatography,and the configuration of CSF in solution was determined by SEC-Malls.The results showed that the CSF of lotus rhizome changed significantly during the heat treatment.The CSF of fresh lotus rhizome in Lu-linhu has the characteristics of high linearity and parallel arrangement.There are many side chain structures in the fresh samples of Miancheng,and the molecules are completely entangled with each other.Heating and acid and alkali treatment mainly affect the length of CSF backbone.In addition,acetic acid treatment can destroy the spiral structure of CSF.Compared with column chromatography,100 KDa ultrafiltration membrane is more suit-able for the purification of CSF.The Mw of CSF in Miancheng is about 2.638×10~7 g/mol,and its molecular structure in the solution is random wire cluster.The Mw of CSF in Lu-linhu is about 2.230×10~7 g/mol,and its molecular structure in the solution is rigid chain.