Food Hydrocolloids| 乙酸强化鲜切胡萝卜片细胞壁果胶酸钙交联：基于果胶免疫标记与钙定位的研究
近日，华中农业大学团队在《Food Hydrocolloids》期刊（一区，IF：12.4）发表题为《Acetic acid strengthens cell wall calcium pectate cross-linking in fresh carrot slices: Insights from pectin immunolabeling and calcium localization》的研究论文。该研究针对罐头胡萝卜热杀菌中细胞壁降解导致的过度软化问题，探究 0.4% 乙酸处理改善质构的作用机制。结果显示，乙酸处理组热处理后硬度为对照组的 3.3 倍，其可抑制纤维素酶等细胞壁降解酶活性，提升果胶甲酯酶活性以促进果胶去酯化，推动内源钙与低酯果胶形成稳定的果胶酸钙交联网络。借助荧光成像与免疫标记等技术，研究证实乙酸能促进游离钙向结合态转化、减少钙流失，最终通过酶调控、果胶去酯化与钙交联网络形成，实现热加工蔬菜质构强化，为清洁标签罐头产品提质提供可行策略。
胡萝卜是全球广泛种植的重要根茎类蔬菜，营养丰富且加工适应性强，罐头制品是其主流即食加工形式。热杀菌是罐头生产的核心工艺，可实现食品商业无菌与常温长期贮藏，但高温处理会引发胡萝卜细胞壁果胶发生 β- 消除降解，导致组织过度软化、口感软烂，同时伴随营养流失与品质劣变，成为制约罐头胡萝卜产业高品质发展的关键技术瓶颈。在清洁标签与感官消费升级趋势下，无外源添加的质构改良技术成为研究热点。已有研究证实，乙酸作为食品级酸度调节剂，能有效调控果蔬细胞壁降解酶活性、抑制果胶热降解，且 0.4% 乙酸在质构提升与风味接受度间达到最优平衡，但其缓解胡萝卜热软化的分子机制、酶调控规律、果胶转化与内源钙交联的协同作用尚未被系统阐明。基于此，本研究以鲜切胡萝卜为对象，解析乙酸介导细胞壁结构稳定的内在机制，为热加工蔬菜质构强化提供理论依据与技术支撑。
0.4% 乙酸预处理的胡萝卜片经 100℃、30 分钟热处理后，硬度达到 2162g，约为蒸馏水浸泡对照组（650g）的 3.3 倍，显著抑制热加工导致的组织软化，质构保留效果优异。
乙酸可显著抑制纤维素酶、β- 葡萄糖苷酶、β- 半乳糖苷酶等细胞壁降解酶活性，阻断细胞壁多糖主链与侧链的降解路径；同时上调果胶甲酯酶（PME）活性，高效催化果胶去酯化，降低果胶甲酯化程度，为钙结合提供充足位点。
乙酸促进胡萝卜内源游离钙离子向结合态转化，去酯化果胶与钙离子通过 “蛋盒模型” 形成不溶性果胶酸钙三维网络；热处理过程中该交联结构稳定存在，有效减少钙离子向蒸煮液流失，提升细胞壁结构强度。
免疫荧光与电镜观测证实，乙酸处理使胡萝卜细胞壁形成连续致密的低酯果胶网络，细胞间黏附力增强，热加工后细胞分离、细胞壁塌陷与变形程度显著降低；同时抑制果胶 β- 消除反应，稳定细胞壁多糖组分分布。
Fig. 1. Effect of different treatment conditions on the thermal processing hardness of Carrots. DWI: distilled water immersion for 9 h; AAI: 0.4% acetic acid immersion for 9 h; DWIC: cooked DWI (100 °C, 30 min); AAIC: cooked AAI (100 °C, 30 min). Different letters indicate significant differences (p < 0.05).
Fig. 2. (a) Hydrogen proton transverse relaxation behavior of carrot slices under different treatment conditions, as determined by low-frequency nuclear magnetic resonance (LF-NMR). (b) Hydrogen distribution in carrots under different treatment conditions. DWI: distilled water immersion for 9 h; AAI: 0.4% acetic acid immersion for 9 h; DWIC: cooked DWI; AAIC: cooked AAI.
Fig. 3. Effects of different treatment conditions on the activity of key cell wall degradation enzymes in carrots. PME: pectin methylesterase; PG: polygalacturonase; Cx: cellulase; β-glu: β-glucosidase; β-gal: β-galactosidase. DWI: distilled water immersion for 9 h; AAI: 0.4% acetic acid immersion for 9 h. Note: Fig. 3(a): The activities of PG, Cx, and β-glu are expressed as the activity per unit fresh tissue weight (μg/(h·g)); Fig. 3(b): The activities of PME and β-gal are expressed as the activity concentration of the enzyme extract (U/mL).
Fig. 4. Degree of methoxylation of pectin in carrot alcohol-insoluble residue under different treatment conditions. Different lowercase letters indicate significant differences between treatments (p < 0.05).
Fig. 5. (a) Scanning electron microscope images of carrot slices from different treatment groups, observed at magnifications of 300 × and 500 × . Abbreviations: ICS, intercellular space. (b) Representative TEM images of carrot tissue and cell walls under different treatments. Abbreviations: CW, cell wall; CM, cell membrane; ICS, intercellular space; ML, middle lamella; OD, osmium droplet; V, vacuole; C, chloroplast. DWI: distilled water immersion for 9 h; AAI: 0.4% acetic acid immersion for 9 h; DWIC: cooked DWI; AAIC: cooked AAI.
Fig. 6. Representative immunofluorescence images of carrot cell walls under different treatments. JIM5 recognizes linear, medium-to-low esterified pectin; LM19 labels highly deesterified or near-acidic pectin; LM20 specifically binds highly methyl-esterified pectin. DWI: distilled water immersion for 9 h; AAI: 0.4% acetic acid immersion for 9 h; DWIC: cooked DWI; AAIC: cooked AAI.
Fig. 7. Total calcium content (mg/g) in freeze-dried carrot powder under different processing conditions. DWI: distilled water immersion for 9 h; AAI: 0.4% acetic acid immersion for 9 h; DWIC: cooked DWI; AAIC: cooked AAI.
Fig. 8. (a) Elemental distribution (C, O, Na, Cl, Ca, K, Mg, P, S) in carrot slices under different treatments. (b) Representative SEM-EDS cross-sectional image of carrot slices. DWI: distilled water immersion for 9 h; AAI: 0.4% acetic acid immersion for 9 h; DWIC: cooked DWI; AAIC: cooked AAI.
Fig. 9. (a) Distribution of free calcium in Fluo-4 AM-labeled carrot slices under different treatment conditions. (b) Calcium ion loss via outward migration (soaking solution and cooking exudate). DWI: distilled water immersion for 9 h; AAI: 0.4% acetic acid immersion for 9 h; DWIC: cooked DWI; AAIC: cooked AAI.
Fig. 10. Effect of calcium ion chelating agent (EGTA) on the hardness of acetate-treated carrots. DWI: distilled water immersion for 9 h; AAI: 0.4% acetic acid immersion for 9 h; DWIC: cooked DWI; AAIC: cooked AAI.
https://doi.org/10.1016/j.foodhyd.2026.112796
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