豬的好口感-酸味（第二章）

2014-2-13 17:09| 發布者: 007畜牧| 查看: 1451| 評論: 2|原作者: 007畜牧

2011年11月21日

作者:Eugeni Roura;Marta Navarro 譯者:劉彩紅

養豬業中酸值是必須研究的一個項目,也有許多文獻是關于這個話題的.通常關于酸作用模式的出版文獻過多地強調”體外”試驗,比如說酸的抗菌能力以及對飼料酸結合力的影響.另外,據稱幼畜體內的酸可以降低胃液的pH值，加強改善飼料中的酶消化。然而，一方面，酸效應對飼料消化的影響的相關數據報道是稀缺的，缺乏一致性。另一方面，算對適口性和飼料采食量的潛在影響力在很大程度上被忽略。這篇報告的目的是為了總結目前已知的關于豬對酸的口感的看法。

很多拿手養豬人都會贊同酸味對豬是重要的感覺。這一點也不奇怪，當我們認識到大多數可能適用于豬的野外自然飼料原料都含有豐富的有機酸。例如，短鏈氨基酸被發現存在于不同的水果中，比如柑橘，野生漿果，蘋果和西瓜中，也包括西蘭花，胡蘿卜，蘑菇，土豆和西紅柿（表1）。檸檬酸酸是最常見的酸，主要存在于水果、塊莖和蔬菜中。其次是蘋果酸和酒石酸。其它商業常用的酸中，有少量的富馬酸，乙酸和甲酸也常常被發現在自然界中常見的食物中。

表1. 食物水果中常見的酸(1)

檸檬酸	蘋果, 杏, 香蕉, 越橘, 藍莓, 雜交草莓, 櫻桃, 越橘,醋栗果, 接骨木漿果, 無花果, 醋栗, 葡萄柚,葡萄,獼猴桃, 金橘,檸檬, 酸橙, 羅甘莓, 橙皮, 橙子,桃, 梨, 菠蘿, 覆盆子, 草莓, 橘子, 楊氏草莓, 豆類, 花椰菜胡蘿卜, 土豆,西紅柿, 大黃.
蘋果酸	蘋果, 杏, 香蕉, 黑莓, 藍莓, 雜交草莓, 櫻桃, 越橘, 葡萄干, 接骨木, 無花果, 醋栗, 柚子, 葡萄, 檸檬,酸橙, 楊梅, 油桃, 越橘, 橙子, 百香果, 桃, 梨, 菠蘿, 李子, 玫瑰果, 榅桲,沙拉, 草莓, 楊氏草莓, 豆類, 花椰菜, 胡蘿卜,豌豆, 土豆，大黃, 西紅柿.
酒石酸	鱷梨, 香蕉, 櫻桃, 葡萄干, 柚子, 葡萄, 檸檬, 酸橙, 梨, 李子.
反丁烯二酸	蘋果, 豆類,胡蘿卜, 蘑菇, 西紅柿.
琥珀酸	蘋果, 藍莓, 櫻桃, 葡萄干, 草莓,豆類, 胡蘿卜, 西紅柿.
乙酸	香蕉 (微量).
甲酸	香蕉 (微量)
乳酸	蘋果

(1) 水果和蔬菜中數量明顯多的酸，采用粗體表示。酸在每種水果或蔬菜中的數量依據品種、成熟度和收獲季節的變化而呈現不同數目。

有機酸可能有兩種影響食欲的感官成分，體感和口感。口腔中的體感是通過三叉神經感知的。從表面上看，跨膜離子通道TRRA1負責感受辛辣，作為疼痛通路（也可以叫傷害性感受器）的一部分。一些酸刺激TRRA1。弱酸，如醋酸，丙酸，甲酸，乳酸在中性pH環境中僅僅部分分離，可能會透過細胞膜，酸化神經元胞質，并刺激傷害性感受器，導致辛辣感和疼痛。然而，強酸如檸檬酸和酒石酸，在三叉水平上是惰性的，沒有或者輕微地引起辛辣反應(Wang等, 2011).因此，弱酸（如醋酸，丙酸，甲酸和乳酸）可能會導致豬的厭惡反應。

發酸味被稱為酸的感知反應，主要通過舌頭的味蕾感受，味蕾通過味覺感受細胞和顱神經VII（鼓索），IX (舌咽神經) 和X (迷走神經)將味覺興奮體連接到味覺皮層. 蛋白質復合物 PKD1L3 和 PKD2L1被激活應答，并負責酸味感受體。然而，因為未分離酸滲透到味覺細胞中，飼料的氫離子濃度和它的酸味感覺之間僅僅有一個中度相關性。Danilova等199年對豬進行的電生理學研究中發現在各種廣泛的潛在味覺興奮劑中，檸檬酸和抗壞血酸引起了豬舌神經的最大反應，但是這些反應與任何行為測試無關。最近，Suarez等2010年使用系統方法評估了飼料添加有機酸和一些鹽如何影響偏食性（圖1）。這些結果顯示，1%的添加水平，檸檬酸和酒石酸顯著地改善了飼料的偏食性，而辛酸、醋酸、磷酸和甲酸引起了厭惡反應。與此相反，添加甲酸鉀鹽沒有任何的厭惡反應。在實際生產中，甲酸和甲酸結合物以及丙酸有一致的效應，它們被報道出能減少飼料的采食量。事實上，市場的大部分已經轉移到有機酸鹽的使用上，弱酸引起了辛辣反應，直至影響采食量，這是市場一部分的沉思。
總之，檸檬酸和酒石酸引發了豬先天就有的酸味喜愛，而且它們的辛辣感覺是微弱的，依然是可以忽略的。它們在飼料中是建議使用的。相反，弱酸如醋酸，甲酸或丙酸引發了軀體的疼痛感受通道，導致對飼料的厭惡反應。除非是使用鹽或者其他包衣形式，否則這些酸因為影響適口性而不能使用在豬的飼料中。

圖1 仔豬對日糧中酸鹽的偏食性(已經經作者同意復制，作者: Suarez等, 動物科學期刊 Vol. 88, E-Suppl. 2: 651, 2010).

*星號表示平均值與中性值50%差異顯著(P<0.05)。

英文

The good taste of pigs (part III): let it be sour

21-Nov-2011

Eugeni Roura Marta Navarro

The use of acids in pig production has merited a lot of research and an even higher amount of literature around it. Often publications regarding the mode of action of acids have overemphasized the relevance of “in vitro” tests such as the antimicrobial activity or the effect on the acid binding capacity of feeds. In addition, acids in young animals have been claimed to decrease gastric pH and hence improve enzymatic digestion of feeds. However, in general the data reported on the effect of acids on feed digestibility is scarce and lacks consistency. On the other hand the potential impact of acids on palatability and feed intake has been overlooked to a great extent. The objective of this report is to summarize what is known today regarding sour taste perception in pigs.

Many people involved in “hands on” pork production will agree that sour taste is of particular relevance in pigs. This is not surprising when we realize that a lot of natural food sources potentially available to pigs in the wild are rich in organic acids. For example, short chain acids are widely found in a variety of fruits like citrus, wild berries, apples and watermelon but also avocados, broccoli, carrots, mushrooms, potatoes and tomatoes (Table 1). Citric acid is the most common of the acids found in fruits, tubers and vegetables followed by malic and tartaric. Among other commercially available acids, small amounts of fumaric, acetic, and formic are also found in foods naturally available in the wild.

Table 1. Main organic acids present in fruits and vegetables (1)

Citric	Apple, *Apricot, Bananas, Bilberry, Blueberries, Boysenberries, Cherries, Cranberries,Currants, Elderberries, Figs, Gooseberries, Grapefruit, Grapes, Kiwifruit, Kumquat,Lemons, Limes, Loganberry, Orange Peel, Orange, Peaches, Pears, Pineapples, Raspberry, Strawberries, Tangerine, Youngberries, Beans, Broccoli, Carrots, Potatoes,Tomatoes, Rhubarb*.
Malic	*Apples, Apricots, Bananas, Blackberries, Blueberries, Boysenberries, Cherries, Cranberries, Currants, Elderberries, Figs, Gooseberries, Grapefruit, Grapes, Lemons, Limes, Loganberry, Nectarine, Orange peel, Orange, Passion fruit, Peaches, Pears, Pineapples, Plums, Rosehip, Quinces, Salad, Strawberries, Youngberries, Beans, Broccoli, Carrots,Peas, Potatoes, Rhubarb, Tomatoes*.
Tartaric	*Avocados, Bananas, Cherries, Currants, Grapefruit, Grapes*, Lemons, Limes, Pears, Plums.
Fumaric	Apples, Bean, Carrots, Mushrooms, Tomatoes.
Succinic	Apples, Blueberries, Cherries, Currants, Strawberries, Beans, Carrots, Tomatoes.
Acetic	Bananas (traces).
Formic	Bananas (traces).
Lactic	Apples.

(1) Fruits and vegetables with significant quantities of the acid are shown in bold and italics. The relative amount of acids in each fruit or vegetable vary widely with the variety, degree of ripeness and seasonal changes of the harvest.

Organic acids have two sensory components that may affect appetence: somatosensing and taste. Somatosensing in the oral cavity is perceived through the trigeminal nerve. Seemingly, the transmembrane ion channel TRPA1 is responsible for perception of pungency as part of the pain pathway (referred to as a nociceptor). Several acids stimulate TRPA1. Weak acids such as Acetic, Propionic, Formic and Lactic are only partially dissociated at neutral pH and may cross the cell membrane acidifying the neuronal cytosol and stimulate the nociceptor leading to pungency and pain. However, strong acids such as Citric and Tartaric, were inert at a trigeminal level resulting in no or insignificant pungency responses (Wang et al., 2011). Thus, weak acids (e.g. Acetic, Propionic, Formic and Lactic) are likely to result in aversive responses in pig.

Sour taste is known for acid perception and is sensed mainly through tongue’s taste buds that connect taste agonists to the gustatory cortex via taste sensory cells and the cranial nerves VII (Chorda Tympany), IX (Glossofaryngeal) and X (Vagus). Protein complexes PKD1L3 and PKD2L1 have been proposed as responsible for sourness perception. However, there is only a moderate correlation between the hydrogen ion concentration of a food and its perceived sourness due to the penetration of non-dissociated acids inside the taste cells. Electrophysiological studies in pigs performed by Danilova et al. (1999) found citric and ascorbic acids to elicit the largest responses in pig taste nerves among a wide group of potential taste agonists but these responses were not linked to any behavioural tests. Recently, Suarez et al. (2010) reviewed in a systematic manner how feed addition of organic acids and some salts affects preferences (Figure 1). The results showed that, at 1% inclusion level, Citric and Tartaric acids significantly improved feed preferences while Caproic, Caprilic, Acetic, Phosphoric and Formic resulted in an aversive response. In contrast, the potassium salt of Formic acid did not show any sign of aversion. In trials performed under more practical conditions Formic acid and combinations of Formic and Propionic acids have consistently been reported to decrease feed intake. The fact that a good part of the market has shifted to the use of the salts of organic acids, may be a reflection, in part, of the effect of weak acids on pungency and ultimately feed intake.

In conclusion, Citric and Tartaric acids trigger an innate sour taste that is attractive to pigs while their pungency is smooth and remains unnoticed. Their use in feeds is recommended. On the opposite side, weak acids such as Acetic, Formic or Propionic trigger the somatic pain pathway and result in aversive responses to feed. Unless presented in the form of some salts or coated, the use of such acids should be avoided in piglet feeds due to palatability issues.

Figure 1. Dietary preferences of acids en salts in piglets. (Reproduced with permission of the authors: Suarez et al., J. Anim. Sci. Vol. 88, E-Suppl. 2: 651, 2010).

*The asterisks indicate that the means are significantly (P<0.05) different than the neutral value of 50 %.

英文來源：pig333.com