The key determinants of food quality are established to achieve the high quality standards that customers expect.
Consequently, there is need to implement measures that will ensure that there exists an environment for continuous improvement.
Every consumer expects that the food products s/he uses will not bring any harm to her/his health and that no economic injury will arise from the use of such products.
Food safety means that the food is free from any harmful physical, chemical, or any microbial contamination at the point of consumption.
Food safety is used in its operational sense e.g. in the canning industry where commercial sterility as applied in low acidity foods is taken to mean the absence of Clostridium botulinum.
To achieve this, there is need to translate the conditions for commercial sterility into a set of heating conditions for a given product in a given package.
Optimization of other quality attributes is only achieved after having first considered the basic aspect of safety.
The key determinants of food quality are propped on several factors such as:
The sensory appeal
Involves features such as the color, the texture, the taste, the smell, etc. of the food sample under consideration.
These are the immediate quality features that an individual recognizes when evaluating a food sample because they are easily perceptible.
An individual is more likely to make a decision on whether to use the food item or not depending on the physically perceptible quality features.
There could be undesirable changes in the texture such as the loss of solubility, loss of water holding capacity, hardening or softening.
The food product may also develop a rancid flavor or any other undesirable off-flavors that may not be very appealing to the consumer.
Changes in color such as darkening, browning or bleaching may not be very desirable in some products that are associated with a specific color.
Sensory appeal thus forms the basis for evaluation and preference by consumers.
The nutritive value
Considers the types and contents of nutrients contained in any given food item. It involves a methodical investigation and may require advanced equipment to perform profiled tests to determine the contents of the nutrients.
This method also includes investigation of the microbial load in the food item as well as the availability of the nutrients profiled and their digestibility.
Some foods may have certain nutrients in abundance but such nutrients remain largely unavailable for uptake by the human digestive system due to degradation.
Storage and processing conditions may lead to loss of certain vitamins, proteins and minerals.
Convenience and the technological quality
Facilitates handling of the food and makes the food items more functional to the manufacturer and the users.
Some of the features that enhance convenience of food items include:
- Shelf life
- Level of processing
- Price – quality relation
- Ease of storage and transportation
- Dimensions of the product
- Functionality/usefulness in the manufacturing of other products.
Some of the chemical and biochemical reactions that may compromise food quality include:
1. Enzymatic browning
Enzymatic browning occurs due to the action of polyphenoloxidase enzyme, which brings about the brown coloration in fruits, seafood, and vegetables.
The effect of enzymatic browning may lead to reduction in the quality of foods, especially during the post-harvest storage time.
Polyphenols are very unstable; therefore, they react with other components in the food to bring about the brown color effect in foods. The reactions are mostly initiated by injuries to the surface of the food sample.
Table 1: Common polyphenols that cause browning (source, www.food-info.net/uk/colour/enzymaticbrowning.htm)
|Apple||chlorogenic acid (flesh), catechol, catechin (peel), caffeic acid, 3,4-dihydroxyphenylalanine (DOPA), 3,4-dihydroxy benzoic acid, p-cresol, 4-methyl catechol, leucocyanidin, p-coumaric acid, flavonol glycosides|
|Apricot||isochlorogenic acid, caffeic acid, 4-methyl catechol, chlorogenic acid, catechin, epicatechin, pyrogallol, catechol, flavonols, p-coumaric acid derivatives|
|Avocado||4-methyl catechol, dopamine, pyrogallol, catechol, chlorogenic acid, caffeic acid, DOPA|
|Banana||3,4-dihydroxyphenylethylamine (Dopamine), leucodelphinidin, leucocyanidin|
|Cacao||catechins, leucoanthocyanidins, anthocyanins, complex tannins|
|Coffee beans||chlorogenic acid, caffeic acid|
|Eggplant||chlorogenic acid, caffeic acid, coumaric acid, cinnamic acid derivatives|
|Grape||catechin, chlorogenic acid, catechol, caffeic acid, DOPA, tannins, flavonols, protocatechuic acid, resorcinol, hydroquinone, phenol|
|Lettuce||tyrosine, caffeic acid, chlorogenic acid derivatives|
|Mango||dopamine-HCl, 4-methyl catechol, caffeic acid, catechol, catechin, chlorogenic acid, tyrosine, DOPA, p-cresol|
|Mushroom||tyrosine, catechol, DOPA, dopamine, adrenaline, noradrenaline|
|Peach||chlorogenic acid, pyrogallol, 4-methyl catechol, catechol, caffeic acid, gallic acid, catechin, dopamine|
|Pear||chlorogenic acid, catechol, catechin, caffeic acid, DOPA, 3,4-dihydroxy benzoic acid, p-cresol|
|Plum||chlorogenic acid, catechin, caffeic acid, catechol, DOPA|
|Potato||chlorogenic acid, caffeic acid, catechol, DOPA, p-cresol, p-hydroxyphenyl propionic acid, p-hydroxyphenyl pyruvic acid, m-cresol|
|Sweet potato||chlorogenic acid, caffeic acid, caffeylamide|
|Tea||flavanols, catechins, tannins, cinnamic acid derivatives|
To prevent enzymatic browning, you can use the following methods
a) Blanching: – short heat treatment to inactivate the enzymes followed by freezing to preserve the quality of the product.
Different enzymes have different inactivation temperatures.
Table 2: Approximated inactivation temperatures of some enzymes
|Enzyme||Effect caused||Inactivation temp. (° C)|
|Lipolityc acyl hydrolase||rancidity||~ 75|
b) Refrigeration and chilling: – storing foods at low temperatures inhibits the enzymes responsible for the browning effect
c) Increasing the acidity of the food: – the low pH is not conducive for the enzyme activity.
d) Dehydration: – the enzymes need sufficient amount of water to work; removing water impedes their capacity to work.
e) Irradiation: – the ionized treatment reduces enzyme activity. However, irradiation may lead to loss of nutrients.
f) Pressurization: – High Pressure Processing leads to enzyme destabilization hence inactivation.
g) Ultra filtration: – will remove large components like polyphenols from the food sample.
h) Treatment with supercritical carbon dioxide: – pressurized liquid carbon dioxide is applied to the food. The resultant carbonic acid lowers the pH of the medium and impedes the activity of the enzymes.
Inhibitors of enzymatic browning
i) Reducing agents such as ascorbic acid, analogs of cysteine, glutathione, and sulphiting agents act by removing oxygen from the medium.
ii) Chelating agents such as phosphates, Ethylenediaminetetraacetic acid (EDTA) and organic acids act by removing metals since most polyphenol oxidase enzymes are metals.
iii) Acidulants such as citric acid and phosphoric acid act by lowering medium pH.
iv) Enzyme inhibitors such as aromatic carboxylic acids, peptides, and substituted recsorcinols react with the enzymes.
2. Non-enzymatic browning
A form of browning effect in foods that is initiated by either Caramelization or Millard reaction. Caramelization happens when the sugars in foods are exposed to high temperatures. Water is removed from the sugar whose isomers are them polymerized.
Millard reaction occurs when the amino acids react with reducing sugars in the presence of heat (can also happen in the absence of heat).
Here, the carbonyl group of the sugar reacts with the amino group in the amino acid to produce melanoidins responsible for various flavors and colors.
Different amino acids produce different flavor components, which makes Millard reaction a key component in the flavoring industry.
Ascorbic acid and metapolyphenols can also contribute to non-enzymatic browning.
Heating leads to formation of furfurals (isomers), which then polymerize to produce the brown color observed as the browning effect.
Millard reactions may reduce the nutritive value of foods. For instance, toasting bread may lead to loss of up to half the protein efficiency ratio of bread.
3. Lipid hydrolysis
Lipid hydrolysis is the breakdown of lipids by addition of water to produce glycerol and fatty acids. This usually happens in an enzyme (lipolytic enzymes such as lipases) mediated process.
The free fatty acids produced by the hydrolysis process may lead to rancidity, which is not desirable in most cases, as the resultant food product will have a poor sensory appeal.
If the hydrolysis occurs in an aqueous sodium hydroxide medium, soap is formed.
Foods most susceptible to hydrolysis include edible oils, margarine, butter, fried foods (potato chips), roasted nuts, dried soups, broths, seasonings, milk, dried meat, frozen fish, etc.
Store foods in a cool and dry place to avoid non-enzymatic browning. Eliminate all lipases to avoid the enzymatic action on the food product.
4. Lipid oxidation
The presence of oxygen in lipid foods will initiate an oxidation process. When the oxidation process is initiated, it will lead to deterioration of the fat phase of the food.
Deterioration of fatty foods is a phenomenon commonly referred to as rancidity.
Uncontrolled oxidation of lipids could lead to formation of several cytotoxic and mutagenic compounds that are harmful to the body.
However, not all oxidative reactions in lipids are bad since the β-oxidation process utilizes lipids to produce energy.
Eicosanoids, which are signaling substances in the body, are also produced through lipid oxidation.
5. Protein denaturation
Involves the alteration of the normal protein structure and a possible destruction of the secondary conformations of such structures.
Some protein denaturation processes are irreversible e.g. cooking an egg. Heat, alcohol, heavy metal salts, acids and bases are some of the agents of protein denaturation.