| Hill potherbs are wild vegetables that grow in the natural environment.Nowadays,hill potherbs are increasingly sought after by consumers for they are pollution free and have good medicinal effects.However,the harvest period of hill potherbs is quite short and they turn yellow very soon.Therefore it is very difficult to preserve them for longer periods.In this experiment,two kinds of potherbs with the highest reserves in Heilongjiang Province were chosen as the research subject:Heracleum modlendouffii(HM)and Aralia elata(AE).This paper explored a number of methods to optimize the pretreatment techniques and freezing storage parameters of these two potherbs,including soaking in crisp-keeping agents,green-preserving blanching pre-treatment techniques,and freezing storage techniques.First,the author chose calcium chloride-sodium alginate as the crisp-keeping agent,and took the blending proportion of calcium chloride and sodium alginate,the concentration of the crisp-keeping agent,and the immersion time as the influencing factors on the content of calcium pectate,crispness,and chewiness of the potherbs.With the blending proportion set at 1:2,concentration of the crisp-keeping agent at 4 g/L,and the immersion time at 30 min,the calcium pectate content in HM was 13.1 mg100/g,and its crispness and chewiness were kept at95%and 90%compared to when it’s fresh.With the blending proportion set at 1:1,concentration of the crisp-keeping agent at 3g/L,and the immersion time at 30 min,the calcium pectate content in AE was 13.8 mg100/g,and its crispness and chewiness were kept90%and 89%compared to when it’s fresh.The author used LSCM to observe the quick-frozen cells and found that cell membrane wall treated by crisp-keeping agent was slightly damaged,and the crispness of the potherb was well preserved.After this,the author treated the potherbs with green-preserving blanching technique.With the blanching time set at 180 s,the temperature at 90℃,and the solid-liquid ratio at 1:11,the absorbance of peroxidase(POD)of HM was 0.001(E=0.17 U/m L)and the yellowing degree(C~2)was 802.51;with the blanching time set at 120 s,the temperature at 95℃,and the solid-liquid ratio at 1:11,the POD absorbance of AE was 0.002(E=0.33 U/m L)and C~2was 870.34.Under such conditions,the yellowing process was suppressed,and the color was well preserved.After pretreating the potherbs,the author explored the parameters in the quick-freezing processing of the potherbs.First,with the anti-freezing solution as the medium,the author drew a standard curve of freezing under ideal conditions.Taking the standard curve as a reference and with the loss of Vc,crispness and chewiness of the potherbs as the indicators,the author determined the technical parameters for quick-freezing processing of these two potherbs using response surface methodology:With the stack height of HM at 3 cm,the initial temperature at-24℃,and wind speed at 3.5 m/s,the percentage of Vc loss was 40.6%,the crispness was 1900 gf,and the chewiness was 1222.85 gf;With the stack height of AE at 3 cm,the initial temperature at-24℃,and wind speed at 4 m/s,the percentage of Vc loss was 31.8%,the crispness was 4505 gf,and the chewiness was 2673.23 gf;Then,the author identified microwave thawing as the optimal thawing method for HM and AE from four different methods.After this,the author analyzed the changes in the loss of Vc,crispness,chewiness,softening ratio,and drying loss ratio of these two potherbs during frozen storage.The following results were observed:water-soluble nutrients showed a downward trend,with no significant change in the loss of Vc,crispness,chewiness,or softening ratio after the stem of HM and AE were frozen for 35d,or after the tuber of AE was frozen for 42d.No significant change in the crispness or chewiness of the tuber of AE was observed after 49d and 42d,respectively;the crispness and chewiness of the stem of AE became stable after 49d.The dry loss ratio of HM and AE rose significantly during the period of 0～42 d and 0～28 d,respectively(P<0.05). |
