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Why people prefer certain foods over others depends largely on a combination of taste and texture. While taste sensations are fairly well understood, scientists are just beginning to unravel the mystery of food texture.
Now, researchers at the Monell Chemical Senses Center in Philadelphia have found that an enzyme in saliva called amylase, which breaks down starch into liquid, could play a key role in determining the appeal of various textures of food. A new genetic study shows that people produce strikingly different amounts of amylase, and that the more of the enzyme people have in their mouth the faster they can liquefy starchy foods.
Scientists think this finding could help explain why people experience foods as creamy or slimy, sticky or watery, and that this perception could affect our preference for foods. For the numerous foods that contain starch, including pudding, sauces and even maple syrup, what can feel just right to some people is experienced as too runny or not melting enough for others because they produce different amounts of the enzyme.
The ability to quickly break down starch, which is a type of carbohydrate, is only one part of the puzzle that determines what people like to eat. Taste preferences are driven by a complicated interaction between taste buds and other receptors in the mouth and nose, and the messages they send to the brain. Culture plays a role, as people tend to like foods that are familiar, says Rick Mattes, a foods and nutrition professor at Purdue University in West Lafayette, Ind. And repetition sometimes can win out: Many people initially don't like oysters because of their slimy texture, for instance, but can come to enjoy them after several tries.
'We all have had the experience of liking a food that someone else complains is too tacky, or slippery, or gritty, or pulpy,' says Paul Breslin, a researcher at the Monell center and a professor at Rutgers University in New Brunswick, N.J. 'This is why a given line of product often comes in different textural forms,' such as orange juice with and without pulp, he says.
Starch comprises or is added to about 60% of the foods people typically eat, so determining how it is digested is key to understanding food-texture preferences, Monell center scientists say. Other research has shown that people have a preference for creamy sensations as well as for foods that start off solid and melt in the mouth such as ice cream and chocolate, says Dr. Breslin, who began the current research because of his interest in creaminess. Amylase also could help explain individual preferences for different brands of ice cream or yogurt, for instance, because they contain different amounts of added starch.
In their recent work, Monell researchers had 73 adults swirl around in their mouths solutions made up of different concentrations of starch -- blobs of translucent gelatinous substances with no particular taste -- and rate their runniness over the course of 60 seconds. Depending on the amount of amylase individuals produced, the starch could be reduced to liquid within seconds.
The researchers also took DNA samples of the participants from a blood sample or cheek swab and studied the link between the numbers of copies of a gene that turns on the production of amylase and how quickly the participant reported the sample turned runny. The findings showed that the number of copies of the gene, called AMY1, varied widely between individuals. People with higher numbers of gene copies reported that the starch turned to liquid more quickly. The study was published last month in PLoS ONE, a journal of the Public Library of Science.
The Monell researchers are now investigating whether people with more AMY1 copies see larger spikes in blood glucose after eating. They also plan to study the link between greater amylase production and food preferences, hypothesizing that people who make more of the enzyme will prefer starchy products because they get a faster blast of glucose into their bloodstream.
The role of amylase and the rate of starch breakdown also has implications for diabetes. People who digest starch quickly could be more likely to have larger spikes in blood-sugar levels and thus a need for the body to generate more insulin. This continued demand on the body might lead these people to become insulin resistant or even diabetic if the body's ability to produce insulin breaks down, says Abigail Mandel, Dr. Breslin's colleague at Monell and first author on the study.
Amylase and other enzymes in saliva could also help explain food-texture preferences that are known to vary with age, Dr. Breslin says. For instance, many young children dislike certain fruits because of a perceived sliminess -- think of the inside of a tomato. But people's saliva-flow rate tends to slow with age, which might affect their ability to break down starch in the mouth and reduce sensations of sliminess.
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人(ren)們(men)之(zhi)所(suo)以(yi)偏(pian)愛(ai)某(mou)些(xie)食(shi)物(wu)，主(zhu)要(yao)是(shi)因(yin)為(wei)食(shi)物(wu)的(de)味(wei)道(dao)和(he)口(kou)感(gan)。科(ke)學(xue)家(jia)們(men)對(dui)味(wei)覺(jiao)的(de)原(yuan)理(li)已(yi)經(jing)有(you)了(le)相(xiang)當(dang)的(de)了(le)解(jie)，但(dan)卻(que)剛(gang)剛(gang)開(kai)始(shi)著(zhe)手(shou)破(po)解(jie)食(shi)物(wu)口(kou)感(gan)的(de)謎(mi)題(ti)。
如今，美國費城蒙內爾化學感覺中心（Monell Chemical Senses Center）的研究人員已經發現，唾液當中有一種名為澱粉酶（Amylase）的(de)物(wu)質(zhi)，這(zhe)種(zhong)酶(mei)可(ke)以(yi)溶(rong)解(jie)澱(dian)粉(fen)，可(ke)能(neng)在(zai)我(wo)們(men)評(ping)價(jia)食(shi)物(wu)口(kou)感(gan)優(you)劣(lie)的(de)過(guo)程(cheng)中(zhong)發(fa)揮(hui)著(zhe)關(guan)鍵(jian)的(de)作(zuo)用(yong)。一(yi)項(xiang)新(xin)的(de)遺(yi)傳(chuan)學(xue)研(yan)究(jiu)表(biao)明(ming)，人(ren)體(ti)製(zhi)造(zao)澱(dian)粉(fen)酶(mei)的(de)數(shu)量(liang)因(yin)人(ren)而(er)異(yi)，互(hu)相(xiang)之(zhi)間(jian)的(de)差(cha)異(yi)大(da)得(de)驚(jing)人(ren)。口(kou)腔(qiang)裏(li)的(de)澱(dian)粉(fen)酶(mei)越(yue)多(duo)，溶(rong)解(jie)澱(dian)粉(fen)食(shi)物(wu)的(de)速(su)度(du)也(ye)就(jiu)越(yue)快(kuai)。
科學家們認為，這一發現有助於解釋，人們為何會對食物產生或滑膩或濃稠、或(huo)粘(zhan)牙(ya)或(huo)鬆(song)軟(ruan)的(de)口(kou)感(gan)，與(yu)此(ci)同(tong)時(shi)，不(bu)同(tong)的(de)口(kou)感(gan)又(you)會(hui)影(ying)響(xiang)我(wo)們(men)對(dui)食(shi)物(wu)的(de)偏(pian)好(hao)。含(han)澱(dian)粉(fen)的(de)食(shi)物(wu)為(wei)數(shu)眾(zhong)多(duo)，其(qi)中(zhong)包(bao)括(kuo)布(bu)丁(ding)和(he)醬(jiang)料(liao)，甚(shen)至(zhi)還(hai)包(bao)括(kuo)楓(feng)糖(tang)。吃(chi)到(dao)這(zhe)類(lei)食(shi)物(wu)的(de)時(shi)候(hou)，有(you)些(xie)人(ren)可(ke)能(neng)覺(jiao)得(de)口(kou)感(gan)剛(gang)剛(gang)好(hao)，另(ling)一(yi)些(xie)人(ren)的(de)感(gan)覺(jiao)則(ze)是(shi)太(tai)過(guo)鬆(song)軟(ruan)，還(hai)有(you)些(xie)人(ren)的(de)感(gan)覺(jiao)又(you)是(shi)不(bu)夠(gou)化(hua)渣(zha)。之(zhi)所(suo)以(yi)會(hui)有(you)這(zhe)樣(yang)的(de)差(cha)異(yi)，原(yuan)因(yin)就(jiu)是(shi)人(ren)體(ti)製(zhi)造(zao)澱(dian)粉(fen)酶(mei)的(de)數(shu)量(liang)各(ge)不(bu)相(xiang)同(tong)。
澱(dian)粉(fen)是(shi)一(yi)種(zhong)碳(tan)水(shui)化(hua)合(he)物(wu)，快(kuai)速(su)分(fen)解(jie)澱(dian)粉(fen)的(de)能(neng)力(li)隻(zhi)是(shi)決(jue)定(ding)人(ren)們(men)食(shi)物(wu)偏(pian)好(hao)的(de)因(yin)素(su)之(zhi)一(yi)。味(wei)道(dao)偏(pian)好(hao)取(qu)決(jue)於(yu)一(yi)個(ge)複(fu)雜(za)的(de)互(hu)動(dong)過(guo)程(cheng)，參(can)與(yu)互(hu)動(dong)的(de)各(ge)方(fang)包(bao)括(kuo)味(wei)蕾(lei)、口腔和鼻腔裏的其他受體，以及所有這些受體發送給大腦的訊息。美國印第安納州西拉斐特（West Lafayette）普渡大學（Purdue University）的食品及營養學教授馬蒂斯（Rick Mattes）說，文化也發揮著一定的作用，因為人們往往會偏愛自己熟悉的食物。除此之外，多次重複有時也會讓人們培養起對特定食物的偏好：以牡蠣為例，很多人一開始都不喜歡它那種粘乎乎的口感，吃過幾次之後卻會喜歡上這種食物。
蒙內爾中心研究員、美國新澤西州新布朗斯維克（New Brunswick）羅格斯大學（Rutgers University）教授布雷斯林（Paul Breslin）說，“我們都有過這樣的經曆，那就是我們喜歡吃某種東西，人家卻覺得這種東西太粘、太滑、太澀或者太軟。正是由於這個原因，同一個產品係列當中往往會有幾種口感不同的產品”，比如帶果粒的橙汁和不帶果粒的橙汁。
蒙內爾中心的科學家們說，我們的日常食品當中，60%由you澱dian粉fen組zu成cheng或huo是shi加jia有you澱dian粉fen，有you鑒jian於yu此ci，要yao想xiang搞gao清qing人ren們men的de口kou感gan偏pian好hao，關guan鍵jian在zai於yu搞gao清qing澱dian粉fen的de消xiao化hua過guo程cheng。布bu雷lei斯si林lin說shuo，其qi他ta研yan究jiu已yi經jing表biao明ming，人ren們men偏pian愛ai滑hua膩ni的de口kou感gan，也ye喜xi歡huan那na些xie入ru口kou即ji溶rong的de食shi物wu，比bi如ru冰bing激ji淩ling和he巧qiao克ke力li。布bu雷lei斯si林lin之zhi所suo以yi投tou入ru目mu前qian的de研yan究jiu，就jiu是shi因yin為wei他ta對dui滑hua膩ni的de口kou感gan很hen有you興xing趣qu。此ci外wai，澱dian粉fen酶mei的de理li論lun也ye有you助zhu於yu解jie釋shi人ren們men對dui冰bing激ji淩ling和he酸suan奶nai酪lao等deng產chan品pin的de品pin牌pai偏pian好hao，因yin為wei不bu同tong品pin牌pai的de產chan品pin加jia入ru了le不bu同tong數shu量liang的de澱dian粉fen。
前些日子，蒙內爾的研究人員讓73名成人品嚐了一些濃度各不相同的澱粉溶液，又讓他們在60秒miao鍾zhong之zhi內nei作zuo出chu評ping價jia，看kan看kan這zhe些xie沒mei有you特te殊shu味wei道dao的de半ban透tou明ming凝ning膠jiao狀zhuang物wu質zhi粘zhan度du如ru何he。這zhe些xie澱dian粉fen可ke以yi在zai幾ji秒miao鍾zhong之zhi內nei溶rong解jie，具ju體ti速su度du則ze取qu決jue於yu各ge人ren製zhi造zao的de澱dian粉fen酶mei數shu量liang。
研究人員還從受試者的血樣和口腔拭子當中提取了DNA樣本，旨在確定負責製造澱粉酶的基因拷貝數和受試者報稱的澱粉溶解速度之間的聯係。負責製造澱粉酶的基因名為AMY1，研究結果表明，不同的人擁有數量千差萬別的AMY1拷貝，與此同時，AMY1拷貝比較多的受試者報稱的澱粉溶解速度也比較快。此項研究於上月發表在公共科學圖書館（Public Library of Science）的《公共科學圖書館•綜合》（PLoS ONE）雜誌上。
目前，蒙內爾中心的研究人員正在進行相關研究，目的是確定進食之後，AMY1kaobeishujiaogaoderenshifouhuichuxianjiaogaodexuetangfengzhi。ciwai，yanjiurenyuanhaijihuazhaochujiaogaodedianfenmeichanliangheshiwupianhaozhijiandelianxi，bingqiejiadingdianfenmeichanliangjiaogaoderenjianghuipianaidianfenhanliangjiaogaodeshipin，yinweitamenkeyirangdaliangputaotanggengkuaijinruzijidexueye。
dianfenmeidezuoyonghedianfenrongjiedesuduyeyutangniaobingyouguan。henyoukeneng，naxienenggoukuaisuxiaohuadianfenderengengrongyichuxianjiaogaodexuetangfengzhi，zheyangyilai，tamendeshentijiubixuzhizaochugengduodeyidaosu。buleisilinboshidemengneiertongshi、研究論文的第一作者曼德爾（Abigail Mandel）說shuo，身shen體ti長chang期qi承cheng受shou這zhe樣yang的de重zhong負fu，這zhe些xie人ren就jiu可ke能neng會hui對dui胰yi島dao素su產chan生sheng抗kang拒ju，如ru果guo身shen體ti製zhi造zao胰yi島dao素su的de能neng力li在zai壓ya力li之zhi下xia陷xian於yu崩beng潰kui，這zhe些xie人ren還hai可ke能neng會hui罹li患huan糖tang尿niao病bing。
buleisilinboshishuo，dianfenmeihetuoyezhongdeqitayixie，haiyouzhuyujieshirenmendekouganpianhaoweishenmehuisuinianlingdebianhuaerbianhua。julilaishuo，xuduonianyoudehaizidoubuxihuanmouxietedingdeshuiguo，yinweitamenjiaodetamenyouzhanyouhua──比(bi)如(ru)西(xi)紅(hong)柿(shi)。不(bu)過(guo)，人(ren)們(men)分(fen)泌(mi)唾(tuo)液(ye)的(de)速(su)度(du)會(hui)隨(sui)著(zhe)年(nian)齡(ling)的(de)增(zeng)長(chang)而(er)衰(shuai)減(jian)。這(zhe)樣(yang)一(yi)來(lai)，他(ta)們(men)用(yong)嘴(zui)巴(ba)溶(rong)解(jie)澱(dian)粉(fen)的(de)能(neng)力(li)就(jiu)可(ke)能(neng)會(hui)受(shou)影(ying)響(xiang)，滑(hua)溜(liu)的(de)口(kou)感(gan)也(ye)會(hui)由(you)此(ci)減(jian)弱(ruo)。
