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Lecture 2

NUTR 3210 Lecture 2: Lecture 2

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NUTR 3210

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NUTR*3210 Lecture 2- September 12, 2017 Food composition analysis • Methods that are used in the chemical analysis of foods (humans) and feeds (animals) • Proximate analysis o Basic determination of 6 components by substraction: 1. moisture, 2. crude protein (Kjedahl analysis of nitrogen) 3. crude fat (ether extract) 4. crude fibre 5. ash (minerals) 6. available CHO (N Free Extract-NFE) o only gives us totals (crude) • Newer method o Replace or extend traditional components of proximate analysis (PA) o i.e total fat, follow up w/ gas chromatography=>individual fatty acids • Southgate/Van Soest Methods o Methods to replace nitrogen free extract (NFE) and Crude fibre for modern CHO labelling Why look at food composition? • Food analysis: the development, application and study of analytical methods for characterizing foods and their constituents o We want to know what is in our food • Why is this important? o Information about foods allow the consumer to make informed decisions o In this course, we start to understand the chemistry of nutrients • Government regulations o Stipulate the “nutrition facts:, “ingredient list”, and “health claims” o Try to eliminate economic fraud • Quality control in food and feeds industries o Ensure consistent food composition for human/companion animal health o Ag settings, encourage optimal animal growth/profitability o Try to eliminate economic fraud by avoiding processors making false claims o Important for quality control Nutrition facts label • How do we get this info • Serving size: how much constitutes 1 serving, how much we are analyzing • Amount per serving: broken down in calories per servings • Total calories: served in every serving size • How much macros in each categories o Broken down, get this info from proximate analysis o Total fat, proteins, and total carbs from proximate analysis • Individual types of fats determined by additional analyses 1 NUTR*3210 Lecture 2- September 12, 2017 • Info about vit and mins: o total minerals from proximate analysis o individual tests for each vit and min • Proximate analysis gets us started on the “bulk part” of our nutrition facts label Proximate analyses (PA) • Early methodology for quantification of nutrients in foods • Tells us what is in our food/crude estimates 1. Moisture content: WATER in the food (determined by drying food) 2. Crude Fat (Determined by ether extract) 3. Ash: minerals, or inorganic portion of the sample 4. Crude protein: Nitrogen content is quantified by the Kjeldahl method (nedd to know this method)* 5. *Crude Fibre: extracted with hot acid and basic salts to mimics stomach and intestinal digestion-> has been replaced w/ NEW METHODS 6. *Nitrogen Free Extract (NFE): all of the above values (#1-5) are subtracted from the initial sample weight to estimate available carbohydrate (Starches and sugars)-> also been replaces w/ NEW methods General comments on proximate analysis • the composition of the food • no information on digestibility • no information on specific amino acids, minerals, lipids, or carbohydrates -> just get TOTAL no information about the COMPOSITIONS o need additional analyses for composition of each nutrient class (CHO, protein, lipids, minerals, vitamins) • Still used in food labelling and animal feed analysis • Has provided the basis for developing more advanced analyses 1. Moisture content ✓ Food sample is oven dried or freeze dried, loss in weight is equal to the moisture content ✓ Errors: the loss of other volatile compounds like volatile fatty acids and alcohols can cause overestimation of moisture ✓ Modern improvement: freeze drying is more accurate than oven drying ✓ Importance ➢ Most further analyses requires a dried sample (think of steps 2-6) ➢ Ag, pets, and animal foods-dry matter basics ➢ Human food labelling is on wet weight, or “as is” basis ➢ Water content is important in human foods, having effects on:  Palatability (dry foods are sometimes less palatable) 2 NUTR*3210 Lecture 2- September 12, 2017  Shelf life (high moisture content may cause foods to spoil, especially in warm environments) ✓ How do we calculate moisture content in foods? ➢ Moisture=water ➢ Food sample(weigh the food=wet weight) ->dry the sample -> dry matter (=dry weight)=moisture content  Remember: Dry matter is the SUM of weights of all nutrients except water ➢ % dry matter=dry weight of sample/wet weight of sample x 100% ➢ % moisture=100-%dry matter 2. Crude fat (or lipids) ✓ Dried food sample is extracted with the non-polar solvent ether to get the lipids out ✓ When ether is dried down (evaporates away) and the lipids/fats remain, and are weighed ✓ Errors: Ether is poor at extracting phospholipids (lipoprotein:lipid + protein), and the method does not identify specific types of fatty acids -> need to use other methods (i.e. gas chromatography) ✓ Goal: to quantify important dietary lipids, including triglycerides (TG), phospholipids (PL), cholesterol and specific fatty acids ✓ Graph: GC trace ✓ What do I need to know about Step 2 of PA: crude fat? ➢ Feed sample -> air dry -> dry matter (=moisture)->ether extraction=crude fat/lipids ➢ Ether extract=crude fat (lipid) content ➢ % crude fat=weight of crude fat/dry weight of sample x 100% ➢ Remember: denominator is written as dry weight, BUT exactly same formula if we use wet weight of the food sample 3. Ash=mineral content ✓ Dried sample (we use a subset/smaller amount of the total dry weight of the food for the PA steps 2-6 b/c we calculate % content) is burned in a high T oven, and the remaining ash is weighed, and it represents the minerals, or inorganic portion of the sample ✓ Errors: this method doesn’t quantify individual minerals ➢ We need separate analysis to determine the individual mineral contnt of the food ✓ “Ash” contains most of the minerals in the sample (i.e. Cl, Zn, Na, Se, Fe, K, Ca, P, Mg, Cr, Mn, Fl, Mb, etc.) ✓ You would need to conduct individual tests to determine the content of each mineral ✓ Importance of knowing the Ash content of a food: 3 NUTR*3210 Lecture 2- September 12, 2017 ➢ Nutritional labelling ➢ Quality and taste of food (i.e. salt improves taste of food) ➢ Microbiological stability ➢ Nutritional requirements ➢ Processing ✓ What do I need to know about Step 3 of PA: crude fat? ➢ See ppt 4. Crude protein/nitrogen: Kjedahl Method ✓ Steps of the Kjeldahl analysis: ➢ Digestion with sulfuric acid, converting all nitrogen in the sample into ammonia/ammonium (depending if 3-4 H), which is then quantified ➢ Multiply grams of nitrogen by 6.25 to get grams of protein ▪ Assume all nitrogen in the food sample is from protein ✓ Errors: ➢ Nitrogen is also liberated from other components like DNA and RNA ➢ Specific amino acids are not determined by this methodology ➢ This method assumes that all proteins have 16% nitrogen. However the actual range is 13-19% nitrogen, so accurate conversion factors vary from 5.3-7 ✓ Modern improvements ➢ Kjeldahl is still in use (with automation), after nearly 20 yrs! If you know the exact % nitrogen in your food protein , you can fine-tune the 6.25 correction factor. Specific a.a. profiles need to be quantified by chromatography ✓ Importance ➢ Protein is an expensive macronutrient in human and animal foods, and accurate analysis is important for human food labelling and ag diet calculations ➢ Want to be precise w/ estimation but can also get away w/ 6.25 ✓ % crude protein=N in sample x 6.25/ dry weight of sample x 100 ➢ Not always exact b/c the amount of N can change in protein sample ➢ Other confounding factor: N can come from other sources ✓ Where do we get 6.25? ➢ Kjeldahl analysis assumption **ALL protein has 16%n nitrogen ➢ 100% (protein)/ 16% (nitrogen)=6.25 ✓ Kjeldhal analysis ➢ Potential errors?  Assumes all proteins have 16% nitrogen ➢ Actual range is 13-19%  Peanuts: 5.46% N  Milk: 6.38% N ➢ Other sources of N (besides protein) 4 NUTR*3210 Lecture 2- September 12, 2017  Nitrates (i.e. deli meats), nitrites, urea, nucleic acids (DNA/RNA), etc all get interpreted as protein What is fibre? • Non-digestible complex carbohydrates (CHO) • Structural part of plants • Fibre is NOT digested in the small intestine, it remains intact. It reaches the colon and is metabolized by microbes in the colon=microbiota • Insoluble o Lignin, cellulose, hemicellulose o Remain intact through intestinal tract to reach the colon o Do not dissolve in water, but colonic bacteria do have enzymes to attack bonds. To a limited degree, will depend on which microbial/microbes live in your colon • Soluble o Pectins, gums, mucilages, hemicellulose o Form gels, fully ferment/metabolize in colon to produce SCFAs (short chains fatty acids) o Dissolve in water, and are susceptible to attack by bacterial enzymes o Colon has very low O2 level=fermentation • Fibre characteristics: o Soluble fibre: ➢ several beneficial effects on human health (i.e. anti-inflammatory) o Insoluble fibre: ➢ digest food spends less time in GI tract ➢ Energy: energy for microbiotia and colon epithelial cells 5/6. Crude fibre and nitrogen free extract (NFE) REPLACED BY Southgate and Van Soest Methods 5 NUTR*3210 Lecture 2- September 12, 2017 ✓ Both of the final 2 fractions of traditional proximate analysis methodology have become obsolete! The underestimate the real fibre content of foods, especially soluble fibres ✓ The NFE (measures carbohydrates) AND all accumulated errors of previous steps -> no good NFE does not differentiate between simple sugars and starches -> unknown CHO composition ✓ Newer methods to evaluate fibre and digestible CHO include(sugars and starches): o Both methods can be used, depending on our needs 1. Southgate method- “s”=sugar and starches a. Quantifies sugars and s
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