Week 3 Food Composition and Function

Why is water important from a food science perspective?

it has a significant impact on the sensory properties of food and it determines the shelf life of a food

What are some properties of water?

liquid at room temperature, freezes at 0 (density increases when freezes), boils at 100 (HB), no smell or taste, universal solvent

What the the types of water in food?

free water, bound water, entrapped water

What is free water?

easily removed by simply pressing or squeezing and has all the physical- chemical properties of water

Why is free water important?

water available in food system which is necessary for chemical and enzymatic reactions

What is free water responsible for in food? 

bacterial growth and for the properties (quality, sensory) of the food

What is bound water?

water bound by other molecules and cannot be easily removed from the food; doesn’t behave as liquid water or act as solvent for salts and sugar

When can bound water be frozen?

very low temperatures (below the freezing point of liquid water)

What are some chemical properties of bound water? 

no vapor pressure- molecules sublimate, always has a higher density than free water

What do the majority of food processes involve?

free water; freezing, drying, emulsification

What is dependent of free water contenet?

growth of bacteria; this is why freezing and dehydration increases the shelf life because it prevents/inhibits bacterial growth 

Why is the importance of water as a solvent also related to free water? 

dissolves molecules, dispersive medium, ionize acids and bases, enzymatic and chemical reactions, heating/cooling medium 

What does water content measure?

how much water exists in the food (mositure)

Why is water content important?

important for monitoring manufacturing, labeling, cooking instructions and strongly affect properties such as texture

What is water activity?

refers to the form in which water exist in a food- its related to free water

Why is water activity important?

help to determine bacterial growth (low aw), shelf stability, moisture migration, clumping/caking 

What does the drying curve of a food tell us?

as time goes on water is more difficult to remove generally 

How does freeze drying work?

frozen foods are subjected to a high vacuum and water is converted directly from the solid phase to the gas phase without becoming liquid

Why is freeze drying desirable?

because it is a way to remove water from foods without degradation

What is a downside of freeze drying?

it’s expensive, high energy intake, firs best for high markets where quality justifies investment and costs

Why is desirable about heat drying?

accelerates moisture removal and supports large scale food production efficiently 

What are the downsides of heat drying?

applying heat can degrade essential nutrients and cause chemical reactions like maillard browning and it can cause the lose of volatile compounds which has an impact on sensory 

What is the buisness trade off of heat drying?

offers operational speed but may reduce product quality, affecting brand reputation and shelf life

What is soft water?

contains low concentration of calcium (Ca2+) and magnesium (Mg2+) ions 

What is hard water? 

rich in calcium and magnesium ions; may also contain iron and other minerals 

What is temporary hardness?

caused by bicarbonates

What is permanent hardness?

caused by sulfates and chlorides (MgSO4, CaSO4, MgCl2, CaCl2)

How do you remove temporary hardness?

by boiling

How do you remove permanent hardness?

chemical treatment (ion exchange with resins, calogon method, etc) boiling doesn’t help

What water tends to be harder?

groundwater

What water tends to be softer?

rainwater

How is hardness commonly expressed?

mg-CaCoO3/L; where lower is softer and higher is harder

How does the increased mineral content in food affect it? 

adding calcium and magnesium alters (positive or negative) the nutritional profile, affect mineral balance for formulation processed foods and beverages 

How does hard water affect the texture, cooking, baking and canning of food? 

can toughen legumes and meats during cooking, dough can be stuffer and less extensible because of calcium and magnesium ions on gluten, interfere with pectin gelation and preservation efficacy 

How can soft water affect the texture cooking, baking and canning of foods? 

promote better hydration and softening of grains and pulses, preferred for consistent dough texture, affect yeast activity and gluten development 

How does hard water affect sensory- flavor and appearance? 

mineral ions can influence taste (bitterness or metallic notes) and may cause cloudiness, films or precipitates in beverages like tea or coffee 

What are the industrial considerations of hard water?

equipment scaling and cleaning challenges, longevity of appliances because of scale buildup, water treatment is often necessary for quality control 

What is vapor pressure?

pressure exerted by the vapor in the surface of the liquid at equilibrium

How does vapor pressure increase?

with temperature

How does vapor pressure decrease?

addition of salts, sugar, etc.

What happens during boiling?

liquid to gas- vapor pressure equals atmospheric pressure

What increases boiling point?

addition of sugar and salts (salts have stronger affect than sugar), external pressure because less molecules can escape from the liquid 

What does freezing do?

safe microbiologically, limits enzyme activity, non-enzymatic changes are slow, good overall shelf life, can maintain fairly easily 

What is the standard for freezing?

-18C

What are the potential quality risks of freezing?

damage from large lice crystals that puncture cell membranes

Why is fast freezing more desirable (liquid N2)?

creates smaller ice crystals = less quality risk

What decreases freezing point?

salts and sugars

What is the triple point?

temperature and pressure at which three phases coexist and equilibrium and will transform phase small changes in temperature and pressure

How does the triple point explain freeze drying?

relies on operating below the triple point of eater so that ice can sublime without becoming liquid 

How does water form solutions?

when small molecules like salts and sugars form homogenous mixtures

When does solubility increase? 

with temperature, especially when hydrogen bonds exist between molecules ex. sucrose is more soluble in hot water than in cold water 

What can solutions be?

ionic or molecular; salts and sugars respectively

What can solutions not be?

separated upon standing or even by filtration

What is a colloid dispersion?

occurs when molecules are too large (1-1000 nm) can’t be dissolved in water but can be dispersed; ie creates a hetergenous mixture 

What are some examples of colloidal systems?

starch, pectins, cellulose, some food proteins

What are the characteristics of colloid stability?

generally stable but still sensitive to temperature and pH changes; changing these conditions may cause gelation or precipitation which can be desirable or undesirable

What is suspension?

occurs when very large molecules/ particles typically larger than 1000 nm form this when mixed with water

What occurs naturally with suspension?

a phase separation, think uncooked starch in water

Most bacteria doesn’t grow when?

aw < .85

Most yeasts and molds can’t grown when?

aw < .5

aw=

vapor pressure food/ vapor pressure of pure water

What happens as the percentage of free water increases? 

aw increases 

What is aw?

measure of the amount of free water available for chemical and enzymatic reactions, represents the energy status of water 

What does the sorption isotherm of food represent? 

moisture content at equilibrium; shows relationship between aw and moisture content at a given temperature 

Why are sorption isotherms useful?

to help determine storage conditions and shelf life of products

How do isotherms help to determine storage conditions and shelf life of products?

by showing how much moisture a food absorbs and under which conditions and determine at which values a food would start to absorb moisture. This helps to determine when to store different foods together, decide if special packaging is needed and determine aw where changes in texture occur  

When are isotherms epically important?

when storing different foods together, when food consists of different parts like crust and filling and understand how moisture will move between those two

How do you find pH?

-log[H+]

What is neutral pH in water?

pH=7=[H+]=[OH-]

How can the amount of acids be determined?

by titration; two foods can have the same pH but different amounts of acids

pOH=

-log[OH-]

pH+pOH=

14

What does the presence of OH- mean?

makes the chance of having [H+] even smaller

Molarity vs Normailty?

Molarity is the number of moles of solute per liter of solution, while normality is the number of equivalents of a reactive species per liter of solution

What is pH scale?

logarithmic

What food properties are affected by pH?

taste, texture and color

Why is pH important for food safety?

low pH prevents bacterial growth and spoilage and many bacteria like E.coli need pH>4.5 to grow 

PH values vary by what? 

optimum pH values used for food production (cheese, vinegar)

What are acid foods?

pH< 4.6 ex. yogurt, lemons, tomatoes

What are acidified foods?

low acid foods where the pH has been adjusted to be lower than 4.6 and aw>.85

What are low acid foods?

have finished equilibrium pH>4.6 and aw>.85 ex. soy, herbs, spices, vegetables, alcohol is the exception 

What is a buffer?

when the pH doesn’t change when we add small amounts of acids or bases

How are buffers used in the food industry?

to maintain food acidity and for product development; optimum activity of enzymes, protein solubility, color, flavor 

What are the two main components of buffers?

a weak acid (HA) and a soluble salt of HA

How do buffers work?

The salt of the acid reacts with added acid capturing H+ and thus are not able to decrease pH. The salt of the acid also reacts with added base to from H2O and conjugate capturing OH- and thus not able to increase pH. 

How to select acid for buffer system? 

want the pKa of the acid close to the desired pH, want the weak acid and it’s conjugate base to be in equal concentrations