Lecture 3 Chemistry of food products of plant origin. Plan

LECTURE 3


Chemistry of food products of plant origin.
Plan:

1. 
   Chemistry of cereals and grain products. Classification, Discovery and Occurrence. Changes in the composition of wheat. Protein content in wheat gluten.
   
2. 
   Opening process. Yeast.
   
3. 
   Chemistry of vegetables and fruits.
   
4. 
   Anthocyanins and flavonoids.
   
5. 
   Canning and freezing vegetables.
   
6. 
   Chemistry of oils and fats.
   
7. 
   Chemistry of sugar products. Sugar substitutes. sucrose. A mixture of glucose and maltose. Syrup.
   

Keys:
https://www.youtube.com/watch?v=yg-fcTyUGjc

Humans have a history of cultivating cereal crops and utilizing their grains to prepare various types of food for thousands of years. The most popular cereal products available in the market include bread, cookies/biscuits, cakes, pasta, noodles, and extruded snacks and breakfast cereals. They are an important part of our daily diets and provide energy and essential nutrients for human health. Cereal grains contain starch and protein as the major components and lipid, non-starch carbohydrates, phytic acid, vitamins, and minerals as the minor components. Physical interactions and chemical reactions occur between these constituents during the processing and storage of cereal products, which determine their quality, storage stability, and nutritional value. With an increasing population of people suffering from celiac disease, diabetes, obesity, and other metabolic syndrome, there are opportunities and challenges for the food industry to develop healthier cereal products through utilizing novel ingredients and improving processing technologies. This book chapter offers a good review of chemical compositions of different cereal grains, processing technologies applied to produce various cereal foods, and future trends of research and product development in this area.
Cereals, in contrast to forage grasses, form a relatively large fruit, termed a caryopsis, in which the fruit shell is strongly bound to the seed shell. The kernel size, which is expressed as grams per 1000 kernels, is not only dependent on the kind of cereal but on the cultivar and crop production techniques, hence it varies widely. In oats, barley, and rice the front and back husks are fused together with the fruit. In contrast, threshing separates wheat and rye kernels from the husks as bare seed. The major constituents of seven kinds of cereal are fairly uniform. Noteworthy variations are the higher lipid content in oats and a lower fiber content in millet and rice. The available carbohydrates consist mainly of starch. Oats are especially rich in nonstarch polysaccharides. These cereals also differ in their vitamin B content. Fruit and seed coats enclose the nutrient tissue (endosperm) and germ in the kernel. Botanically the endosperm consists of the starchy endosperm (70–80% of the kernel; and the aleurone layer, which, with exception of barley, is a single cell layer. The aleurone layer is rich in protein and also contains fat, enzymes and vitamins. The proteins, of which half are water-soluble, appear as granules in the aleurone cells.
The starchy endosperm is the source of flour. Its thin-walled cells are packed with starch granules which lie imbedded in a matrix which is largely protein. A portion of these proteins, the gluten proteins, is responsible for the baking properties of wheat. The concentrations of the proteins and some other constituents (vitamins and minerals) decrease from outer to inner cells of the endosperm. The germ is separated from the endosperm by the scutellum. The germ is rich in enzymes and lipids shows that wheat milling, when starchy endosperm cells are separated from germ and bran, results in a substantial loss of B-vitamins and minerals.


Special Role of Wheat–Gluten Formation

After addition of water a viscoelastic cohesive dough can be kneaded only from wheat flour. The resulting gluten, which can be isolated as a residue after washing out the dough with water, removing starch and other ingredients, is responsible for plasticity and dough stability. Gluten consists of 90% protein, 8% lipids and 2% carbohydrates. The latter are primarily the water-insoluble pentosans, which are able to bind and hold a significant amount of water, while the lipids form a lipoprotein complex with certain gluten proteins. In addition, enzymes such as proteinases and lipoxygenase are detectable in freshly isolated gluten. The gluten proteins, in association with lipids, are responsible for the cohesive and viscoelastic flow properties of dough. Such rheological properties give the dough gas-holding capacity during leavening and provide a porous, spongy product with an elastic crumb after baking. Rye and other cereals cannot form gluten. The baking quality of rye is due to pentosans and to some proteins which swell after acidification and contribute to gas-holding properties.