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Chemical components determine how food fuels human life.

Foods consist of dry matter and water, with dry matter split between organic compounds and mineral ash. Carbohydrates like starch and cellulose supply energy, while nitrogenous protein compounds construct tissue and drive protoplasmic functions. Laboratory combustion isolates mineral ash, exposing the elemental foundation of plant and animal tissue. Understanding these distinct chemical fractions allows dietary choices to be evaluated for both physical efficiency and cost savings.

PREFACE → CHAPTER I

Fats and organic acids modulate heat production and digestion.

Fats provide two and a quarter times as much heat per gram as starch, serving as concentrated energy reserves composed of stearin, palmitin, and liquid olein. Organic acids such as malic in apples and citric in lemons yield no heat but stimulate digestive secretions and enhance palatability. Essential oils impart characteristic aromas without adding calories, while complex protein molecules carry sixteen percent nitrogen alongside carbon and oxygen. Balancing these non-nitrogenous energy sources with protein ensures complete physical maintenance.

CHAPTER II → CHAPTER III

Fresh vegetables and fruits deliver essential acids and hydration.

Vegetables supply high moisture and specific carbohydrates while remaining indispensable for normal intestinal action. Sweet corn deposits protein early in growth, whereas tomatoes contain soluble sugars and malic acid that can be lost if juice is discarded. Raw vegetables require careful washing or brief immersion in boiling water to kill surface bacteria from contaminated soil. Fruits contribute fruit sugar alongside organic acids that enhance digestion, making them vital dietary adjuncts despite low protein levels.

CHAPTER IV → CHAPTER VI

Legumes, nuts, and dairy provide dense protein and fat.

Legumes like beans and peanuts yield substantial protein, though their fiber demands extended intestinal work for full digestion. Nuts act as concentrated foods rich in fats and energy, with chestnuts supplying starch while pecans and almonds deliver high fat and nitrogen. Milk serves as a complete food containing fat, casein, albumin, and milk sugar suspended in eighty-seven percent water. Fat is the most variable constituent in milk, driving the primary difference in energy yield between rich and poor samples.

CHAPTER VII → CHAPTER VIII

Meat composition depends on animal age, cut, and preparation.

Connective tissue and muscle tube thickness determine meat toughness, which softens during rigor mortis as natural lactic acid develops. Pork contains the highest fat content among meats, offering concentrated fuel in bacon and ham at lower relative cost than beef. Boiling meat shrinks its bulk primarily through water loss, while extracting only four percent of total nutrients regardless of initial water temperature. Leaner cuts often match expensive cuts in protein, making structural texture the main driver of market price.

CHAPTER IX → CHAPTER X

Roller milling separates wheat kernel fractions to produce flour.

Hard spring wheats yield glutinous flour suitable for bread, whereas soft winter wheats contain more starch. Modern roller milling uses sequential breaks and silk sieves to isolate refined flour middlings from tough outer bran. High-grade patent flour captures seventy-two percent of the grain's weight, leaving low-grade red dog and offal for livestock feed. Elastic gluten formed by gliadin and glutenin determines whether ground flour expands into light, structured bread.

CHAPTER XI

Fermentation transforms flour proteins and carbohydrates into leavened bread.

Yeast converts soluble sugars into carbon dioxide gas and alcohol, inflating the elastic gluten network to expand the loaf. Extracted gliadin transforms workable dough into a brittle mass resembling putty, proving that specific gluten balance governs loaf volume. Prolonged fermentation volatilizes small amounts of nitrogen compounds and slightly oxidizes flour fat without reducing overall nutritive value. Adding starch to strong flour alters dough texture, whereas excess gluten fails to increase loaf size beyond the gluten's binding limit.

CHAPTER XII → CHAPTER XIV

Tea and coffee act as digestive stimulants rather than systemic foods.

Green tea retains raw tannin through quick roasting, while black tea undergoes fermentation that decomposes tannin and alters leaf color. Both tea and coffee derive their stimulating properties from alkaloids like theine and caffeine, which elevate arterial pressure and alter sensory awareness. Coffee contains high fat and caramelized sugars formed during roasting, yet contributes negligible digestible nutrients to a meal. Commercial adulteration frequently introduces spent leaves, roasted cereal grains, or chicory to disguise inferior tea and coffee stock.

CHAPTER XV → CHAPTER XVI

Monetary economy in diet depends on nutrients purchased per unit cost.

Calculating digestible nutrients per dime reveals that milk, flour, oatmeal, and dried beans offer significantly more fuel and protein than expensive meat cuts. Ten cents spent on milk at standard prices yields more protein, fat, and total calories than the same sum spent on sirloin or round steak. Protein deserves priority when selecting dietary staples, but excess protein converts inefficiently to energy that carbohydrates supply at far lower cost. Evaluating food by chemical yield rather than bulk weight prevents economic waste in family meal planning.

Fig. 56.—Composition of Foods.

Balanced dietary rations match nutrient intake to physical labor.

Heavy manual labor demands wide rations rich in energy-dense fats and carbohydrates, whereas sedentary work requires lower total caloric intake. Standard dietary guidelines specify daily protein and calorie thresholds, though individual nitrogen equilibrium can often be maintained on lower protein inputs. Dividing daily food into three regular meals maintains a steady nutrient supply and prevents the overeating common in two-meal schedules. Abruptly restricting food intake forces the human body to consume its own muscular tissue rather than drawn-up reserves.

CHAPTER XVII → CHAPTER XIX

Pure drinking water requires physical boiling or filtration to neutralize pathogens.

Mineral salts in groundwater create hard or alkaline conditions that irritate the digestive tract and diminish water's solvent capacity. Decaying organic matter generates nitrites and free ammonia through bacterial action, indicating dangerous surface drainage contamination. Waterborne pathogens like typhoid bacilli persist in surface streams and lakes, causing severe disease outbreaks when ingested without heat treatment. Boiling water serves the same protective purpose as cooking food, destroying invisible microorganisms that natural sedimentation leaves behind.

CHAPTER XX → CHAPTER XXI

Quantitative laboratory experiments verify food purity and chemical composition.

Heating food samples in drying ovens reveals exact moisture content, while burning residues in muffle furnaces isolates inorganic mineral ash. Nitric acid reactions identify nitrogenous proteins by forming yellow xanthoprotein, and alkali titrations measure organic acidity in fruit juices. Microscopic inspection distinguishes intact starch granules in raw potatoes from inflated, ruptured grains in cooked tissue. Chemical tests using specific reagents detect adulterants such as cottonseed oil, synthetic vanilla resins, and artificial coal tar dyes.

CHAPTER I → CHAPTER X

Systematic review questions consolidate principles of food chemistry and digestion.

Critical evaluation of baking powders compares cream of tartar residues against residual aluminum and phosphate minerals in baked goods. Vinegar production relies on sequential alcoholic and acetic fermentations that convert fruit sugars into dilute acetic acid. Spices contribute volatile essential oils that stimulate appetite without contributing direct caloric value to a ration. Digestibility coefficients measure the exact percentage of ingested protein, fat, and carbohydrates absorbed by the human digestive tract.

CHAPTER XI → CHAPTER XX

Applied chemical science elevates household efficiency and agricultural practice.

Practical application of chemistry to home management connects soil fertility, crop production, and dairy management to human health. Comprehensive agricultural literature links land selection, tillage methods, animal nutrition, and household sanitation into a single scientific discipline. Educating students in food evaluation promotes nationwide physical efficiency while reducing unnecessary household expenditure. Standardized legal frameworks protect public access to educational texts, ensuring scientific knowledge reaches readers across all institutions.

Professor of Agricultural Chemistry, University of Minnesota…

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Human Foods and Their Nutritive Value

Master the chemical foundation of diet, food composition, cooking dynamics, and economic nutrition.

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