(香港中文大學知識轉移項目基金Knowledge Transfer Project Fund──驅動社會影響項目Social Impact Driven Project 特稿七)
相信大家都有吃過果醬，甚至有自行製作的經驗。自製果醬的材料和步驟看似簡單，只需要把水果、糖和檸檬汁加熱煮至濃稠，入樽後冷卻就成了凝膠狀的果醬。果醬之所以能成形主要靠果膠(Pectin)，它是由半乳醣醛酸(Galacturonic acid)組成的多醣聚合物，是構成植物果實細胞壁的結構及硬度的物質。由於它不能被人體消化吸收，所以也屬於膳食纖維。煮果醬時，加熱會破壞細胞壁以釋出果膠，而糖會吸走水份，之後加入酸性檸檬汁以促進果膠聚合成立體網狀、內含液體的彈性凝膠──果醬。
水果果膠種類多 品種熟度皆影響
果醬是早期人們用以保存水果的方法，早在16世紀時已有記載。而果膠卻在近二百年前(1825年)被法國化學家發現，多年來都被用作天然食物添加劑。在水果未熟時，果膠還是不溶的原果膠(Protopectin)前體，令水果較硬。隨著水果成熟，原果膠會被轉化成水溶、能凝固成「啫喱」狀的果膠，令水果變得較軟及有彈性。但當水果過熟時，果膠會分解為果膠酸(Pectic acid)，令水果變得更軟、失去彈性、「出水」等。原果膠能在煮果醬時轉化成果膠，但果膠酸卻不能變回果膠，故做果醬的水果宜生不宜熟。有些水果如蘋果、紅莓、杏等，果膠含量較多，能直接用於製作果醬。低果膠水果如車厘子、提子等要製成果醬，則需要加入高果膠水果同煮，或直接加入已提煉的果膠。蘋果肉渣及柑橘皮分別含15-20%和30-35%果膠，這些製作果汁的副產品通常被物盡其用來提煉果膠。
果膠通常以脂化度(Degree of esterification)作分類。高脂化度果膠需要高濃度及較酸性環境(pH<3.5)才能凝膠，凝膠較挺身及脆，多用作製作啫喱、糖果、甜品、果醬等。低脂化度果膠凝膠只需適當濃度的鈣，所需的pH幅度亦較寬(pH2-6)，凝膠較軟而多被加入飲品增稠，或製作低糖果醬。果膠除了用作改善食品質感外，不少研究指出，果膠對穩定血糖、血脂，以至腸道健康都有所裨益。
果膠控糖降血脂 益菌利腸助抗炎
歐洲食品安全局(European Food Safety Authority, EFSA)在審視多份不同地區、不同時間的研究報告後指出，成年人每天攝取至少6克果膠，有助維持血液膽固醇正常，而每餐攝取至少10克果膠則能減低餐後血糖波動。
荷蘭有研究邀請27名輕微高血脂患者，每天多攝取15克果膠或纖維素(Cellulose)。四週後，吃果膠組別的血液總膽固醇(Total cholesterol, TC)、三酸甘油脂(Triglycerides, TG)及低密度膽固醇(LDL-C)都有明顯下降，而服用高脂化度及高份子量(Molecular weight)果膠組別的效果更為明顯。果膠和大部分水溶性纖維一樣，能吸收膽汁酸(Bile acid)，與之結合並透過排便帶出體外，引發身體運用儲存的膽固醇製造更多膽汁酸，從而降低血液的低密度膽固醇(壞膽固醇)及總膽固醇水平，而不會影響高密度膽固醇(好膽固醇)。有實驗分別測量高分子聚糖如果膠、幾丁聚醣(Chitosan)及海藻酸鈉(Alginate)與膽汁酸的結合能力，發現果膠和腸道膽汁酸脫氧膽酸(Sodium deoxycholate) 有特異性結合能力(Specific binding)，即是果膠對於清除這種膽汁酸特別有效，從而加強改善血脂的效果。
果膠除能改善血脂外，亦可穩定血糖。有研究以藥物令小鼠患上糖尿病，再以不同份量的橘皮果膠餵食四週。四週後，服食中至高劑量果膠小鼠的胰島素抗性指數(HOMA-IR)及餐後血糖都明顯降低，而果膠的劑量越高，穩定餐後血糖的效果越明顯。研究團隊指出，果膠能降低餐後血糖的效果，不只因它能在吸收水份後和食物混合並增加稠度，從而減慢小腸吸收糖份，更因它能調控胰島素及血糖代謝，從而穩定血糖。果膠亦能直接調控腸道中的免疫細胞、減少炎症細胞因子如TNF-a、IL-1、IL-6等分泌，有抗炎作用。
丹麥有研究以健康人士的腸道菌，以果膠培植24小時。發現腸道益菌如青春雙歧桿菌 (Bifidobacterium adolescentis)及普拉梭菌 (Faecalibacterium prausnitzii)在果膠培植下都有明顯上升，而在年輕受試者的腸道菌中更為明顯。有益短鏈脂肪酸如丙酸(Propionic acid)和丁酸(Butyric acid)在果膠及年輕受試者腸道菌的培植下，水平明顯上升。另有研究以果膠或纖維素餵飼小鼠四週，發現果膠組別血液中的短鏈脂肪酸乙酸明顯較多，而大腦中的腦源性神經營養因子 (Brain-Derived Neurotrophic Factor, BDNF)亦有明顯上升。研究指出，服用果膠能影響腸道菌，令血液中的短鏈脂肪酸增加，從而增加大腦BDNF水平，改善腦神經健康。
一般新鮮水果蔬菜平均含約1%果膠，故每天需吃約500-600克才能達至維持血液膽固醇水平健康的效果，當然亦可食用營養補充劑作補充。新鮮水果蔬菜所含的有益物質不只有果膠一種膳食纖維，敬請繼續留意我們的介紹。
參考資料/延伸閱讀:
＜益生第一關＞2024/03/27--『蘋果最好連皮吃 四季常吃保健康』
https://hskgene.com/blogs/probiolife-first/apple?_pos=5&_sid=c40b35bad&_ss=r
＜益生第一關＞2024/08/07--『夏日新興凝膠食品 飽腹利腸有助健康』
https://hskgene.com/blogs/probiolife-first/fiber_jelly?_pos=1&_sid=b17cfb72b&_ss=r
＜益生第一關＞2021/01/22--『膳食纖維種類多 腸道菌最佳拍檔』
https://hskgene.com/blogs/probiolife-first/dietaryfiber_microbiome?_pos=3&_sid=2c182256e&_ss=r
Easy Reading:
果醬製作掌握4關鍵！青蘋果、橘子最適合新手，謹記「基本公式」比例是美味秘訣|Yahoo News| 12-04-2022
為何做果醬沒有「酸」不行、棉花糖竟然不是素的？ |食力foodNEXT| 08-05-2022
https://www.foodnext.net/science/knowledge/paper/5098734120
Pectin recipes | BBC Food |
https://www.bbc.co.uk/food/pectin
The science and magic of jam-making | Biochemistry and molecular biology | The Guardian |10-03-2013
https://www.theguardian.com/science/blog/2013/oct/03/science-magic-jam-making
The short, sweet, and sticky history of jam| National Geographic | 04-26-2024
https://www.nationalgeographic.com/history/article/history-of-jam-meghan-markle-lifestyle
Google Images:
學術論文：
Lara-Espinoza C, Carvajal-Millán E, Balandrán-Quintana R, López-Franco Y, Rascón-Chu A. Pectin and Pectin-Based Composite Materials: Beyond Food Texture. Molecules : A Journal of Synthetic Chemistry and Natural Product Chemistry. 2018;23. doi:10.3390/molecules23040942
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6017442/
Wandee Y, Uttapap D, Mischnick P. Yield and structural composition of pomelo peel pectins extracted under acidic and alkaline conditions. Food Hydrocolloids. 2019;87: 237–244. doi:10.1016/j.foodhyd.2018.08.017
https://www.sciencedirect.com/science/article/abs/pii/S0268005X18304946
Freitas CMP, Coimbra JSR, Souza VGL, Sousa RCS. Structure and Applications of Pectin in Food, Biomedical, and Pharmaceutical Industry: A Review. Coatings. 2021;11: 922. doi:10.3390/coatings11080922
https://www.mdpi.com/2079-6412/11/8/922
Sozaeva DR, Dzhaboeva AS, Shaova LG, Tsagoeva OK. The pectin content in different types of fruit crops and their physicochemical characteristics. Vestn Voronež gos univ inž tehnol. 2016; 170–174. doi:10.20914/2310-1202-2016-2-170-174
https://www.vestnik-vsuet.ru/vguit/article/view/914?locale=en_US
Li D, Deng L, Dai T, Chen M, Liang R, Liu W, et al. Ripening induced degradation of pectin and cellulose affects the far infrared drying kinetics of mangoes. Carbohydrate Polymers. 2022;291: 119582. doi:10.1016/j.carbpol.2022.119582
https://www.sciencedirect.com/science/article/abs/pii/S0144861722004878?via%3Dihub
Scientific Opinion on the substantiation of health claims related to pectins and reduction of post-prandial glycaemic responses (ID 786), maintenance of normal blood cholesterol concentrations (ID 818) and increase in satiety leading to a reduction in energy intake (ID 4692) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal. doi:10.2903/j.efsa.2010.1747
https://www.efsa.europa.eu/en/efsajournal/pub/1747
Brouns F, Theuwissen E, Adam A, Bell M, Berger A, Mensink RP. Cholesterol-lowering properties of different pectin types in mildly hyper-cholesterolemic men and women. European Journal of Clinical Nutrition. 2012;66: 591–599. doi:10.1038/ejcn.2011.208
https://www.nature.com/articles/ejcn2011208
Massa M, Compari C, Fisicaro E. On the mechanism of the cholesterol lowering ability of soluble dietary fibers: Interaction of some bile salts with pectin, alginate, and chitosan studied by isothermal titration calorimetry. Frontiers in Nutrition. 2022;9. doi:10.3389/fnut.2022.968847
https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2022.968847/full
Liu Y, Dong M, Yang Z, Pan S. Anti-diabetic effect of citrus pectin in diabetic rats and potential mechanism via PI3K/Akt signaling pathway. International Journal of Biological Macromolecules. 2016;89: 484–488. doi:10.1016/j.ijbiomac.2016.05.015
https://www.sciencedirect.com/science/article/abs/pii/S0141813016304238
Elshahed MS, Miron A, Aprotosoaie AC, Farag MA. Pectin in diet: Interactions with the human microbiome, role in gut homeostasis, and nutrient-drug interactions. Carbohydrate Polymers. 2021;255: 117388. doi:10.1016/j.carbpol.2020.117388
https://www.sciencedirect.com/science/article/abs/pii/S0144861720315617
Gu F, Larsen N, Pascale N, Petersen SA, Khakimov B, Respondek F, et al. Age-related effects on the modulation of gut microbiota by pectins and their derivatives: an in vitro study. Frontiers in Microbiology.2023;14. doi:10.3389/fmicb.2023.1207837
https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1207837/full
Tang X, De Vos P. Structure-function effects of different pectin chemistries and its impact on the gastrointestinal immune barrier system. Critical Reviews in Food Science and Nutrition. 2023; 1–15. doi:10.1080/10408398.2023.2290230
https://www.tandfonline.com/doi/full/10.1080/10408398.2023.2290230#abstract
Blanco-Pérez F, Steigerwald H, Schülke S, Vieths S, Toda M, Scheurer S. The Dietary Fiber Pectin: Health Benefits and Potential for the Treatment of Allergies by Modulation of Gut Microbiota. Current Allergy and Asthma Reports. 2021;21: 43. doi:10.1007/s11882-021-01020-z
https://link.springer.com/article/10.1007/s11882-021-01020-z
Church JS, Bannish JAM, Adrian LA, Rojas Martinez K, Henshaw A, Schwartzer JJ. Serum short chain fatty acids mediate hippocampal BDNF and correlate with decreasing neuroinflammation following high pectin fiber diet in mice. Frontiers in Neuroscience. 2023;17. doi:10.3389/fnins.2023.1134080
https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2023.1134080/full
You might also like...
乳鐵蛋白結合有機鐵 長者溫和補鐵新方案
早餐對健康好重要 更助調節生理時鐘
