Extraction, Properties And Application Of Low Methoxyl Pectin From Silkworm Excrement

Silkworm excrement was a byproduct of sericulture, which was often used as animal feed or fertilizer. Siklworm excrement was rich in protein, carbohydrate and pectin. It was a potential pectin resource. In this paper, pectins were extracted from silkworm excrement by means of acid extraction and molysite precipitation. The rheological and gelling properties of the pectin were studied. Low methoxyl pectin(LMP) andhigh methoxyl pectin(HMP) were mixed to prepare a fat substitute(FS) which was used in low-fat mayonnaise.A single factor experiment and an orthogonal test were used to optimize the production conditions. The optimal conditions for pectin production were determined to include extraction: oxalic acid solution,p H 1.5, solid-liquid ratio1:20(g/m L), 60 min at 85 ℃, and precipitation: 0.50% molysite solution at p H 3.5. Under the optimal conditions, the yield of the pectin was 5.93±0.05%, the methoxy content and the degree of esterificationwere5.62±0.04% and 34.46±0.06%, respectively. The content of total galacturonic acid of the pectin was 69.58±0.31%. The results of FT-IR was consistent with the physical and chemical results. Thus, the quality of the pectin was absolutely acceptable.The rheological properties of the pectin were studied. The results showed that the pectin solution was a typical pseudo plastic fluid. The viscosity of pectin solution increased with the increasing of pectin, sugar and calcium concentration, but decreased with the increasing of temperature. And with the increasing of p H value, the viscosity of pectin solution increased at the beginning, then decreased from p H 4.0.The gel strength of the pectin were studied to optimize the gelling conditions. And the optimal gelling conditions were as follows: pectin concentration 3.0%~3.5%, p H 4.0, calcium concentration 30~40 mg/g pectin, sugar content 20%~30%, 5 ℃, 36 h. Compared with commercial LMP, the gel strength of silkworm excrement LMP was relatively wake. So,LMP from silkworm excrement could be used in those food which needed low gel strength or mixed with high gel strength pectins, such as citrus pectin.Based on water holding capacity, gel strength and elasticity, the gel conditions of LM-HM mixed gelwere optimized, which showed that LMP:HMP=1:1, sugar content 45%,pectin 1.0% and calcium concentration 30 mg/g pectin. FS prepared with LM-HMmixed gel contributed to dehydration and aggregation which were solvedeffectively by adding 0.10%CMC.The rheology, texture and sensory properties of low-fat mayonnaise determined the best fit addition of the FS was 20%.