Effective Learning and Teaching of Home Economics / Technology and Living Series:

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Effective Learning and Teaching of Home Economics / Technology and Living Series:

Food Preparation and Cooking Skills with Meal Planning in Basic Food Science

5

^th

July, 2016

Ms. Ivy Ng

Adjunct Lecturer at HKU SPACE Registered Dietitian, UK

MSc in Dietetics & Human Nutrition Former President, HK Nutrition Association

Former Chairperson & Founder, HKU SPACE Human Nutrition & Dietetics Alumni

(2)

Topics

• Gelatinisation of starch

• Dextrinisation of starch

• Denaturation of protein (gluten) in wheat flour

• Raising agents in flour dough

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Gelatinisation of Starch

• Takes place under moist heat

• Starch granule swells

• Loss of amylose from the swelling granule

• Gelatinisation temperature depends on the type of starch

• Produces a thick cooked paste

• e.g. thickener for sauces

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Gelatinisation of Starch

• Amylose molecule • Amylopectin molecule

(5)

Gelatinisation of Starch

• Swelling and disorganisation of starch granules heated in water

• Measures of gelatinisation

• Swelling of granules

• Increased viscosity (thickness or stickiness)

• Increased translucency

• Increased solubility

(6)

Gelatinisation of Starch

• Factors affecting gelatinisation

• Ratio of amylose to amylopectin

• Amount of water

• Heating time

• Presence of other substances

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Dextrinisation of Starch

• Takes place under dry heat

• Thermal degradation of starch

• Browning occurs

• Different from Maillard reaction in which amino acid is involved

• Such starches produce thin cooked pastes

• Little thickening power, e.g. brown gravy

• Example: toast a slice of bread in toaster

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Denaturation of Protein (Gluten) in Wheat Flour

• Proteins are amino acid polymers

• Denaturation is a process in which proteins lose the quaternary structure (three-dimensional structure of multiple polypeptides), tertiary structure (three-dimensional structure) and secondary

structure (hydrogen bonds between peptide group chains) which are present in their native state

• Primary structure (linear structure of amino acids) is intact

• Protein can be denatured by:

• Application of some external stress

• Compound such as a strong acid or base

• Concentrated inorganic salt

• Organic solvent (e.g., alcohol or chloroform)

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Denaturation of Protein (Gluten) in Wheat Flour

• Flour does not contain gluten

• Flour contains two proteins (glutenin and gliadin)

• When water is added to flour, gluten is formed

• Gluten requires mixing to form a strong continuous network

• Fully developed dough should form a uniformly thin, smooth film without tearing

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Denaturation of Protein (Gluten) in Wheat Flour

• When batters and doughs are baked, most of the moisture evaporates or is absorbed by gelatinising starch granules.

• Loss of moisture, presence of heat, gluten sets into a firm and rigid yet porous structure that holds its shape

• Egg protein, when heated, also set into a firm, rigid structure

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Raising Agents in Flour Dough

• Raising agents, also known as leavening agents, cause baked goods to rise

• Providing lightness and volume to baked goods

• Leavened baked goods are more porous and tender

• During baking, heat causes matter to change from one physical form to another

• Solid to liquid (butter melts)

• liquid to gas (water to vapour)

• Molecules move faster and spread farther apart

• This expansion is the basis for leavening

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Raising Agents in Flour Dough

• There are three main leavening gases in baked goods:

• Steam

• Air

• Carbon dioxide

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Raising Agents in Flour Dough

Steam (water vapour), gaseous form of water

• A physical leavener

• Forms when water, milk, eggs, syrups, or any other moisture- containing ingredient is heated

• e.g. choux pastry is leavened almost exclusively by steam

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Raising Agents in Flour Dough

Air

• A physical leavener

• Added to batters and doughs by physical means, by:

• Creaming

• Whipping

• Sifting

• Folding

• Kneading

• Stirring

• Sponge cake and angel food cake contain eggs that are whipped, and this adds volumes of air to the batter.

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Raising Agents in Flour Dough

Carbon dioxide

• Although it is present in air, in trace amounts only

• It is formed from two sources:

• Yeast fermentation, which is a biological leavener

• Chemical leavening agents

• Baking powder

• Baking soda

• When carbon dioxide is warmed from the heat of the oven, it moves into existing air bubbles, causing them to expand.

• Breads and cookies are examples of baked products that rely on carbon dioxide to raise

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Raising Agents in Flour Dough

• Yeast are usually applied in baked goods with presence of wheat (gluten), so that porous and rigid structure can be formed

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Raising Agents in Flour Dough

Baking powder

• Acidic

• Made by combining soda and a dry acid, such as cream of tartar

• Milder by 2-3 times

Baking soda

• Alkaline

• Stronger

• Reacts with acid to produce bubbles

• Usually used in products

containing buttermilk, brown

sugar, yoghurt, lemon juice, cocoa powder, etc.

• Overuse produces metallic aftertaste

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Q&A

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家政科／科技與生活科有效的學與教系列：

處理和烹調食物的技巧與膳食計畫 - 食品科學基礎

2016年7月5日

Ms. Ivy Ng

Adjunct Lecturer at HKU SPACE Registered Dietitian, UK

MSc in Dietetics & Human Nutrition Former President, HK Nutrition Association

Former Chairperson & Founder, HKU SPACE Human Nutrition & Dietetics Alumni Auditor, ISO 22000:2005 Food Safety Management Systems

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課題

• 澱粉的糊化作用

• 澱粉的糊精作用

• 小麥粉中的蛋白質變性（麵筋）

• 粉糰的發麵劑

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澱粉的糊化作用

• 在潮濕的熱力下發生

• 澱粉的顆粒膨脹

• 直鏈澱粉從膨脹顆粒流失

• 糊化溫度取決於澱粉的種類

• 產生濃稠的糊

• 例如：醬汁的增稠劑

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澱粉的糊化作用

• 直鏈澱粉分子 • 支鏈澱粉分子

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澱粉的糊化作用

• 澱粉顆粒在水中受熱，膨脹，並解體

• 測量糊化

• 顆粒膨脹

• 粘度增加（稠度或粘性）

• 透明度增加

• 溶解度增加

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澱粉的糊化作用

• 影響糊化的因素

• 直鏈澱粉與支鏈澱粉的比例

• 水的份量

• 加熱時間

• 其他存在的物質

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澱粉的糊精作用

• 在乾熱下發生

• 澱粉熱降解

• 澱粉變褐色

• 有別於涉及氨基酸的梅納反應

• 這種澱粉產生稀薄的糊

• 稠化能力較弱，例如肉汁

• 例子：烘麵包器烤烘麵包

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小麥粉中的蛋白質變性（麵筋）

• 蛋白質是氨基酸聚合物

• 變性是一個過程，其中蛋白質失去四級結構（三維多肽的結構），

三級結構（立體結構）和二級結構（肽基鏈之間的氫鍵），其存在於它們的天然狀態

• 一級結構（氨基酸線性結構）是完整的

• 蛋白質變性原因：

• 使用一些外加壓力

• 化合物，如強酸或強鹼

• 濃縮的無機鹽

• 有機溶劑（例如，醇或氯仿）

• 輻射

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小麥粉中的蛋白質變性（麵筋）

• 麵粉不含有麵筋

• 麵粉中含有兩種蛋白質（谷蛋白和醇溶蛋白）

• 麵粉加入水後，產生麵筋

• 麵筋需要經過混合來形成一個強大的連續網絡

• 充分混合的粉糰應該形成一個均勻、薄、光滑的膜並且沒有撕裂

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小麥粉中的蛋白質變性（麵筋）

• 當麵粉糊和粉糰被烤焗時，大部份的水份被蒸發或由糊化澱粉顆粒吸收。

• 當麵筋流失水份，且有熱力的存在時，形成一個硬而堅固但多孔的結構，能夠保持形狀

• 當雞蛋中的蛋白質遇熱，也形成一個堅固的結構

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粉糰中的發麵劑

• 發麵劑，又被稱為膨鬆劑，可令烘焙食品膨脹

• 為烘焙食品提供鬆軟度和增加體積

• 膨鬆了的烘焙食品比沒有膨鬆的較多孔和鬆軟

• 在烘焙時，熱力使物質從一種物理形態改變為另外一種

• 固體變為液體（牛油溶解）

• 液體變為氣體（水變為水蒸汽）

• 分子活動較快，彼此之間的距離也較遠

• 這種擴張，就是膨鬆的原理

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粉糰中的發麵劑

• 在烘焙食品中，有三種令食物膨鬆的氣體：

• 蒸汽

• 空氣

• 二氧化碳

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粉糰中的發麵劑

蒸汽（水蒸汽）是水的氣態形式

• 是一物理性膨脹劑

• 當水、牛奶、雞蛋、糖漿或任何其他含水的成分被加熱時便形成

• 例如：蛋油鬆皮，幾乎完全是透過蒸汽令批皮膨鬆

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粉糰中的發麵劑

空氣

• 是一物理性膨脹劑

• 以物理形式被添加到麵粉糊和粉糰內：

• 擂油

• 打起

• 篩

• 拌入

• 搓

• 攪勻

• 海綿蛋糕和天使蛋糕包含打起了的雞蛋，增加了麵粉糊的空氣含量

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粉糰中的發麵劑

二氧化碳

• 雖然存在於空氣，但只佔微量

• 從兩個來源形成：

• 酵母發酵，是一種生物膨鬆劑

• 化學膨鬆劑

• 發粉

• 食用梳打粉（碳酸氫鈉）

• 當焗爐的溫度上升時，二氧化碳變暖，並移動到已存在的氣泡中，

使氣泡膨脹

• 麵包和曲奇是依靠二氧化碳而膨脹的烘焙產品例子

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粉糰中的發麵劑

• 酵母通常應用於含有小麥（麵筋）的焙烤食品中，它讓多孔和堅固結構可形成

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粉糰中的發麵劑

發粉發粉發粉發粉

• 酸性

• 由梳打粉及乾酸，如撻撻粉組合而成

• 溫和了2-3倍

食用食用

食用食用梳打粉梳打粉梳打粉梳打粉

• 鹼性

• 較強

• 與酸產生反應，產生氣泡

• 通常用於含酪乳漿、黃糖、酸奶酪、檸檬汁、可可粉等的產品

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