Food Preservation
Why do we exhaust cans before sealing?
Drives out oxygen, increases volume of can so a vacuum can form
What are the two types of emulsions and an example of each?
Oil in water: Mayo, everything
Water in oil: Butter and margarine
Define Isoelectric point.
The pH at which the protein carries a net zero charge.
How is Carrot Cake typically leavened?
What kind of off flavors/colors can this type of leavening produce?
Baking Soda!
Soapy flavor, greenish hue, good volume, but can degrade vitamins
What different preparation methods would you use for a less-tender vs. a more-tender cut of meat?
Less - slow moist heat. longer at lower temp.
More - more quickly, dry heat
Why is it important to freeze quickly?
How does thermal vs. freezing affect the microbial load?
Water will crystallize before it can migrate and less structural damage will occur.
Thermal is to destroy pathogenic spores. Freezing does not lower the microbial count.
What changes occur when eggs are stored?
What happens when boiled eggs are overcooked?
pH increases, air cell enlarges, thick white decreases, vitelline membrane stretches and yolk flattens. Minimize via. refrigeration.
The yolk turns green due to ferrous sulfate.
What is the pH range and sugar range of good fruit jelly?
2.8-3.4, 40-70%
Describe the difference between the following flours in how they work with gluten formation.
Cake Flour, Bread Flour, Soy Flour, Wheat flour, Fresh wheat flour
Cake - very low protein, low gluten
Bread - high protein, high gluten
Soy - has lipoxygenase and will increase S-S bonds and structure
Wheat - already aged and has some s-s bonds already
fresh wheat - has not developed the s-s bonds already, will have a weaker structure
What is the effect of Nitrites on meats?
Preservation and curing and PINK color
At higher altitudes, what changes need to be made in canning?
Longer processing time due to lower boiling point.
What are the two primary ways starch molecules are hydrolyzed in food systems?
Acid + heat
Enzymes (amylase)
What are two of the three ways to form a curd?
Direct acid addition, rennet, bacterial fermentation
Describe the mixing sequence for a cake and how that effects leavening.
First, cream butter and sugar then add eggs, then dry ingredients.
Creaming disperses fat and incorporates air, which creates the lift needed.
How can tenderness be measured?
A warner bratzler shear press
What is blanching and why is it used?
Quick heating of food, with a rapid cooling step to stop cooking before freezing.
Primarily, it is used to inactivated degradative enzymes before freezing. It can also reduce microbial load, remove air from tissues, and soften veggies to make them easier to pack.
Explain the following concepts:
Emulsifier (specifically the structure)
Permanent vs. Temporary Emulsion
Conductivity meter
Emulsifier: has polar and non polar groups that allow it to hold the phase boundaries together by reducing interfacial tension
P vs. T: Temp. has a low emulsifier content and eventually separates (salad dressing). Permanent has high emulsification and high viscosity (ranch)
Conductivity: oil doesn't conduct charge, water does. You can use this to determine the continuous phase.
What are three ways to get a protein precipitate?
Why won't a gel form with fresh pineapple?
Add alcohol, salt out, extreme pH
It contains bromelain, a natural protease which will break down amino acids.
How is gluten formed?
How do the following affect gluten development?
Sugar, Salt, Fat, Baking Soda?
Hydration and mechanical work
Sugar - competes for water, prevents hydrophobic interactions, weakens structure
Salt - neutralizes charge repulsions, strengthens bonds between proteins
Fat - coats and inhibits water absorption, decrease in structure
Soda - increases pH, interferes with protein interaction, poor gluten formation
Why is the cooking temperature higher for ground beef vs. whole meat cuts?
The inside of an animal is sterile. So there is less chance of contamination. The contamination comes from the processing. ground beef has been processed a lot more so it needs more cooking to be safe.
Why is waxy maize important in freezing starches?
Ice crystal growth with degrade the starch network. Waxy starches contain amylopectin only and don't form solid gels, which will enable a stable freeze-thaw.
What is the iodine test for starch?
Iodine is added to a starch system, resulting in a color change. The degree of color change is related to the amount of amylose in starch. More amylose = more blue color.
Why do many pectin gels require a lot of sugar?
With LMP, why can low sugar gels form?
There is a monolayer of water around pectin, so we need a high amount of sugar to compete for the water so the pectin bonds can form and create a gel.
Calcium bridges allow low sugar gels to form with LMP molecules, which are very spreadable.
Miscellaneous Topics!
Which common carbs can yeast not metabolize?
What are the two components of gluten?
How do double acting baking powders work?
Lactose and starch
Glutenin and gliadin
They contain both fast and slow acting acids, which allows for leavening over a wide temp and long period of time.
What are the two factors of toughness or tenderness?
Presence of collagen connective tissue and coagulation of muscle fiber during cooking.
Tender meats are low in connective tissue and muscle fiber coagulation is limited in quick cooking.
Tough meats have more connective tissue and must be cooked at lower temps to prevent coagulation.