Unit 2 Flashcards
What is proximate analysis?
basic determination of 6 components by subtraction, don’t get specific AA, minerals, lipids or CHO, just get totals
What do the southgate/van soest methods replace?
NFE and crude fibre for modern CHO labelling
What are the 6 steps to proximate anaylsis?
- moisture content - water in food (determined by drying)
- crude fat (total fat) - via ether extract
- ash (minerals/inorganic portion of sample)
- crude protein (N content is quantified via Kjeldahl method)
- crude fibre (type of CHO) - extracted via hot acid & basic salts ** NEW METHODS **
- available CHO (nitrogen free extract NFE) - all the above values are subtracted from initial sample weight to estimate available CHO ** NEW METHODS **
Describe the process, errors, and importance of Moisture content
process: food sample is dried (oven/freeze), loss in weight = moisture content
errors: loss of other volatile compounds (VFAs & alcohols) = overestimation of moisture (modern improvements: freeze>oven)
importance: most further analysis (#2-6) require a dry sample, agriculture systems work with food data on DM basis (human: weight weight/”as is” basis)
* water content has an affect on palatability & shelf life in human foods
How is moisture content calculated?
%DM = (dry weight of sample / wet weight of sample) * 100
% moisture = 100% - %DM
Describe the process, errors and the goal of crude fat (step 2)
process: dried food sample is extracted with non-polar solvent ether to get liquids out (or ether is dried down (evaporates) and lipids/fats remaining are weighed)
errors: ether is poor @ extracting phospholipids & method does not identify specific types of FA
goal: to quantify important dietary lipids (incl. triglycerides (TG), phospholipids (PL), cholesterol & specific FAs)
How is crude fat calculated?
% crude fat = (weight of crude fat / dry weight of sample) * 100
Describe the process, errors and importance of ash (step 3)
process: dried sample is burned in a high temp oven & remaining ash is weight - represents the minerals/inorganic portion of the sample
errors: method doesn’t quantify individual minerals - need separate analysis to determine individual mineral content of food
importance:
- nutritional labeling
- quality & taste of food
- microbiological stability
- nutritional requirements
- processing
How is ash calculated?
% ash = (weigh of ash / dry weight of sample) * 100
Describe the process, errors, modern improvements, and importance of crude protein/nitrogen (Kjeldahl method) (step 4)
process: digestion with sulfuric acid, converting all N in sample to ammonia, which is then quantified, multiple grams of N by 6.25 to get grams of protein
errors: nitrogen is also liberated from other components like DNA, RNA; specific AAs are not determined via this methodology
modern improvements: if you know the exact %N in your food protein, you can fine-tune 6.25 correction factor; specific AA profiles need to be quantified via chromatography
importance: protein = expensive macronutrient in human & animal foods + accurate analysis is important for human food labeling & agricultural diet calcualtions
how is crude protein calculated?
% crude protein = (N in sample*6.25 / dry weight of sample) * 100
where does 6.25 come from?
kjeldahl analysis assumption: all protein has 16% N
100% (protein) / 16% (N) = 6.25
therefore N x 6.25 = CP
what are potential errors of assuming a factor of 6.25?
- assumes all proteins have 16% N
- actual range is 13% - 19 %
(other sources of N: nitrates & nitrites, urea, nucleic acids)
What is fibre?
- non-digestible complex carbohydrate (CHO)
- structural part of plants
- fibre is NOT digested in SI (remains intact until reaches colon)
Describe insoluble fibre
ex. lignin, cellulose, hemicellulose
- speeds up rate of movement of gut contents (decreased transit time - digested food spends less time in GIT)
- helps control intestinal pH, which can benefit microbiota
- increased laxation (passage of feces)
- reduces risk of diverticulitis, colon cancer
- provides some energy thru SCFA production - energy for microbiota & colon epithelial cell
describe soluble fibre
ex. hemicellulose, pectins, gums, mucilages
- can bind with cholesterol & bile acids to decrease absorption
- can slow stomach emptying, which may slow digestion of simple starches and sugars (decreased glycemic index)
- provides significant energy & maintains colon & microbiota health thru fermentation & release of SCFAs - several beneficial effects on human health (e.g. anti-inflammatory)
What is step 5 - crude fibre/NFE replaced by? why?
Southgate & Van Soest methods
NFE measured all carbohydrates AND all accumulated errors of previous steps (not good); does not differentiate b/w simple sugars & starches –> unknown CHO composition
What is the southgate method?
quantifies sugars & starches & TOTAL fibre
but no breakdown of soluble vs. insoluble fibre types - only tells total fibre
what is the van soest method?
differentiates & quantifies b/w soluble vs insoluble types of fibre (cellulose + hemicellulose, lignin)
provides a poor differentiation of sugars & starches important for ruminants that consume high fibre diets
what method is recommended for human food labeling? for agriculture systems?
southgate = human
van soest = agricultural
what is NFE?
- nitrogen free extract
= digestible CHO - measured by subtractions of all other components (steps 1-5)
- potential errors: NFE accumulates ALL errors that exist for the other components of PA
What are the 4 types of digestion systems?
- simple system (non-functional caecum)
- simple system (functional caecum)
- ruminant system
- avian system
what are the components in the GIT?
mouth, esophagus, stomach, SI, caecum, LI, rectum
what is a digestive system?
GIT + all associated organs (liver, pancreas, gallbladder) which provide & store various secretions (typically enzymes) required for digestion
Describe the simple system with “non-functional caecum”
e. g. human, pig, cat, dog
- monogastric
- non-functional caecum = appendix
- suited for a nutrient dense, low fibre diet
- human digestive tract = ~16 ft
- lipid digestion: liver & gall bladder
Describe digestion for a monogastric (non-functional caecum) in the oral cavity
- food is chewed
- 2 enzymes secreted in saliva:
- alpha-amylase (breaks down starches into glucose)
- lingual lipase (starts breakdown of lipids)
Describe digestion for a monogastric (non-functional caecum) in the stomach
- via pepsin & HCL
- acidic compartment (pH ~2) kills bacteria, denatures proteins
- 2 sphincters:
- entrance: lower esphageal sphincter
- exit: pyloric sphincter - elastic (empty = 50mL, filled = 1-1.5L)
- gastric glands secrete: H2O, mucus (protect stomach & coat food), electrolytes, HCL, enzymes –> all referred to as gastric juice
- digesting/denatured food = chyme
- gastric emptying = 2-6hrs
Describe digestion for a monogastric (non-functional caecum) in the SI
- duodenum, jejunum, ileum
- main site for nutrient digestion & absorption (if miss this point, no opportunity for absorption)
- intestinal motility (longitudinal & circular - impeding waves) of 2 different types of muscles
- circular muscles squeeze inwards towards lumen
- longitudinal muscles squeeze inwards from either end - chyme acidity neutralized by pancreatic juice (pH 2 —-> pH 7 (basic secretions))
- pancreas: provides secretions that neutralize stomach acid
- digestion of food via pancreatic juice (basic, lots of enzymes) and bile acids (lipid digestion)
Describe absorption in the SI for simple systems with non-functional caecums
- gross folds (kerckring folds) - increase SA 3 fold
- villi - increase SA 10 fold
- microvilli - on each cell (enterocyte) - increase SA by another 20 fold
- total: ~1000 fold increase in SA
- lacteal: lymph vessel (important for lipid absorption)
How are nutrients transported across an enterocyte?
- diffusion: no energy required, needs a concentration gradient
- facilitated diffusion: requires a transporter (passive transport), needs a concentration gradient
- active transport - ATP is needed to maintain a [ ] gradient across membrane
Describe digestion for a monogastric (non-functional caecum) in the LI (colon)
- fermentation of fibre occurs to produce SCFAs (energy source for colonocytes)
- fermentation of fibre by colon bacteria
- water & electrolyte absorption/reabsorption
- low O2 levels in colon
What is the microbiota?
- collection of ALL the bacteria that reside in an established environment
what is the microbiome?
ALL the genetic material found within the microbiota (bacteria genome)
Describe the simple system with a functional caecum
e. g. horse, rabbit, hamster
- functional caecum
- suited for diet with large amounts of forage
- digestion takes place in hindgut (large functional caecum & LI (colon)) - produce SCFAs
How does digestion work in the simple system with a functional caecum?
- enormous hindgut with bacteria for breakdown of most fibres to sugars & SCFAs
- also produces various vitamins thru action of bacteria in caecum
- LI is 45% of horses digestive tract so LONG transit times
- slow transit times = max breakdown of nutrients and absorption
- up to 70% energy for horse comes from SCFAs
Describe the ruminant/multiple system
e. g. cattle, sheep, goat
- foregut fermentation
- presence of large stomach divided into 4 sections: rumen, reticulum, omasum, abomasum
- system suited to very high roughage diets
Describe digestion in the reticulum
- honeycomb appearance
- traps foreign materials (wire, nails, etc.)
- rich in bacteria
Describe digestion in the rumen
- largest section of the stomach
- rumen papillae - increased SA for absorption
- rich in bacteria - 60-80% of energy from SCFA are produced & absorbed here
Describe digestion in the omasum
- reabsorption of water & some electrolytes
- filters large particles
Describe digestion in the abomasum
- “true stomach”
- digestive enzymes secreted from gastric glands
What are the advantages and disadvantages of the ruminant system?
advantages:
- vitamin synthesis
- bacterial synthesis of essential AA
- mineral availability
- NPN utilization
disadvantages:
- “destruction” of available CHO, protein
- heat and gas production
Describe the avian system
e. g. chicken, turkey
- beaks & claws are important for breaking up foods into smaller pieces that birds can swallow
- light in order to fly
- rapid digestion - short transit time
- birds are “sight” feeders - poor sense of taste & smell
How does digestion work in the avian system?
crop
- enlarged area of esophagus, serves as temp storage location for food
two chambered stomach
- glandular portion = proventriculus, gastric enzymes + HCL secreted (&mucus)
- muscular portion = gizzard, muscular contractions to help breakdown food, grind + digest, pick up small rocks
small intestine
- site of nutrient absorption
ceca (2 large cecums)
- minor site of bacterial fermentation
large intestine
- very short, serves mainly to connect SI to cloaca
- storage of undigested material
- water & electrolyte absorption
cloaca
- where digestive, urinary & reproductive systems meet
- uric acid mixes with feces
what is digestibility?
measure of the fraction of a specific nutrient or of energy that is extracted by the GI tract
how is digestibility calculated?
calculate coefficient (b/w 0 & 1), multiply this # by 100 = % digestibility
calculated from amount of nutrient in diet & amount appearing in feces
Describe the total collection method
- allow animal to adapt to diet (7-21 days)
- isolate animal for qualitative analysis
- measure intake over 3-10 day period
- collect & weigh all feces
- analyze feces for amount of nutrient of interest that is still in feces
How is the apparent digestibility coefficient calculated?
ADC = (total intake - total feces) / total intake
what is apparent digestibility
assumes that all of the contents of the feces are non-digested material originating from the diet
Describe the indicator method
- “marker technique”
- requires that a specific component in the food can be identified as a marker
- marker can be internal (natural component of feed) or external (component added to feed)
- characteristics of a good marker:
- should be non-absorbable & move through GIT uniformly
- must not alter GIT function
- must mix well with the other food/feed components
- must be easily & accurately measured in feed & fecal samples
what is true digestibility
- perform digestibility study using TEST DIET (collect feces) containing nutrient X
- switch to diet free of nutrient X, collect feces
- subtract level of nutrient X in feces of animals fed zero nutrient diet from test diet
How is true digestibility calculated?
true/accurate digestibility of nutrient X = test diet fecal content of nutrient X - zero nutrient diet content of X
