Processing of cocoa beans: Fermentation

The beans embedded in mucilaginous pulp are removed from the fruit pods and subjected to microbial fermentation as the first stage in the preparation of chocolate.

Cocoa bean fermentation is still a spontaneous curing process to facilitate drying of nongerminating cocoa beans by pulp removal as well as to stimulate color and flavor development of fermented dry cocoa beans.

The fermentation of cocoa relies on a complex succession of bacteria and filamentous fungi, all of which can have an impact on cocoa flavor.

During cocoa bean fermentation, the role of micro-organisms is limited to removal of the pulp that surrounds the fresh beans and the production of indispensable metabolites. The former includes pectin de-polymerization by yeasts.

The latter encompasses anaerobic yeast fermentation of sugars to ethanol, microaerophilic fermentation of sugars and citric acid to lactic acid, acetic acid and mannitol by lactic acid bacteria (LAB), and aerobic exothermic bioconversion of ethanol into acetic acid by acetic acid bacteria (AAB). These microbial activities result in the death of the bean due to penetration of mainly ethanol and acetic acid through the husk into the cotyledons.

These biochemical changes inside the beans contribute to the reduction of bitterness and astringency and the development of flavor precursors. Cocoa flavor precursors are developed during fermentation and drying of cocoa beans. Polyphenols and alkaloids contribute to astringency and bitterness of cocoa and chocolate.

Cocoa beans are mainly fermented in heaps enveloped in plantain leaves or in wooden trays. Yeasts dominate at the beginning, and up to 24 h of fermentation.

Their most important roles are to break down the citric acid in the pulp, which leads to an increase in pH; to produce ethanol and organic acids, which kill the bean cotyledons to produce volatile organic compounds that contribute to precursors of chocolate flavor; and to secrete pectinases, which reduce the viscosity of the pulp and allow aeration of the pulp mass.

Fermentation has several purposes:
*Facilitates the removal of the viscous pulp around the beans and their subsequent drying;
*Contributes to the color and flavor development of the nongerminating cocoa beans, as it avoids embryonic growth and activates hydrolytic bean enzymes, enabling the expression of the flavor potential of the cocoa beans genetically and enzymatically
*Reduces the bitterness and astringency, in particular by exchange of compounds through diffusion between the cocoa bean cotyledons and the environment.
Processing of cocoa beans: Fermentation

Chemical reactions during coffee roasting

A coffee bean has a porous structure consisting of cellulose, arabinogalactans, lignin, oils,and other organic compounds. Within this porous structure, there are biological cells containing aromatic compounds, water, and various gases.

Green coffee beans lack the colour and characteristicaroma of roasted coffee; both are formed during the roasting process.

During roasting process, the coffee beans change colour from green to a dark brown, and the main coffee aroma compounds are developed. Additionally, the coffee beans increase in size, as well as lose most of their moisture content.

Maillard reaction
A key reaction for the development of roasted coffee flavor and color is the Maillard reaction. At temperatures from 150-200°C, carbonyl groups (from sugars) and amino groups in proteins react to form aroma and desirable flavor compounds. Heat speeds up the reaction.

The change in color is due to the production of melanoidins. Humic acids or melanoidins, as final products of the Maillard reaction between amino acids and monosaccharides; they are the brown-colored substances that impart to roasted coffee its characteristic colour.

Strecker Degradation
The reaction is dependent on other compounds created during the Maillard reaction. Strecker degradation is a reaction between an amino acid and an α-dicarbonyl with the formation of an aminoketone that condenses to form nitrogen hetero-cyclic compounds or reacts with formaldehyde to form oxazoles. Strecker degradation also contributes to the brown color of the coffee.

Carbon dioxide is quantitatively the most important non-aroma-contributing volatile compound in roasted coffee. It is generated by pyrolysis and the Strecker degradationreaction. The amount is dependent on the degree of roast and can be up to 10 ml /g coffee.

Caramelization of Sugars
From 170-200°C the sugars in coffee start caramelizing, which browns the sugar and releases aromatic and acidic compounds. This process converts complex sugars into more simple sugars. This is a non-enzymatic reaction, meaning that it takes place only in the presence of heat. This reaction continues until the end of the roast and it also contributes to the sweet notes in the coffee’s aroma, such as caramel and almond ones.

Chemical reactions during coffee roasting

Tea withering process

Physically withering is partially reduces moisture content and conditions the leaf physically and biochemically for the subsequent stages of manufacture.

The withering of tea leaves is the first step in processing black tea. The loss of water in fresh leaves makes it easier for the subsequent rolling and fermenting.

During this stage, the cell sap become more concentrated and cell membrane permeability increases.

In tea withering, green tea leaves are spread over a wire-netted platform and trough. A fan driven by induction motor pushes air from below the platform to dry the tea leaves. During this withering process water vaporizes and the rate of water evaporation is related to the humidity and temperature.

Withering optimization can take anywhere from 6 hours under artificial air and temperature conditions up to 18 hours under natural conditions.

Withering will increases the amino acids for aroma formation, caffeine for cup character, and organic acids for flavor.

Chemical withering is the key process for formation of white tea color, essential to activate the enzyme polyphenol oxidase and peroxidase for color development of white tea.
Tea withering process

Ripening of cheese

Cheese ripening is a slow and consequently an expensive process. It us a biochemical process which takes place under physical, microbial and enzymatic conditions. A nearly tasteless raw cheese is converted into a smooth, tasty finished product having characteristics properties.

The expense of cheese ripening arises principally from the inventory cost associated with holding a large amount of cheese in storage and the capital cost of providing a ripening facility adequate to hold sufficient cheese during ripening.

Traditionally, cheese was ripened in caves or cellars, probably at 15-20°C for much of the year.

Since the introduction of mechanical refrigeration for cheese-ripening rooms in the 1940s, the use of a controlled ripening temperature has become normal practice in modern factories.

Ripening usually involves the softening of cheese texture, as a consequence of the hydrolysis of the casein matrix, changes in the water-binding of the curd and changes in pH.

Cheese reacts by a hydrolytic denaturation through various stages, which can take place simultaneously, proceeding until the stage of basic molecules, i.e. amino acid.

During ripening, cheese flavor develops due to the production of a wide range of sapid compounds by the biochemical pathways.
Ripening of cheese

Vitamins as antioxidants in processed foods

Vitamins as antioxidants in processed foods
Oxidation, a series of chemical reactions yielding undesirable and products (off odors, colors, and flavors), may occur in many fruits and vegetables and foods high in fat and oil during exposure to air, light, heat, heavy metals, certain pigments or alkaline conditions. Enzymatic browning may occur in some fruits and vegetables, particularly apples, banana, peaches, pear, and potatoes, which contain phenolase enzymes. When these fruits and vegetables are cut or sliced and exposed to air, the phenolases catalyze oxidation of phenolics compounds to ortho-quinone compounds, which then polymerize, forming brown pigments.

Oxidation in lipids (autoxidation) and in fat and oil containing foods, on the other hand, occurs as a result of the susceptibility of fatty acids (building blocks of fats and oils) to oxidations and subsequent formation of reactive compounds referred to as “free radicals”.

The free radicals promote the development of a series of chemical reactions which lead to the production of off-flavors, colors, odors, and rancidity. While both saturated and unsaturated fatty acids are susceptible to oxidation, unsaturated fatty acids are significantly more susceptible than their saturated counterparts at room temperatures and at elevated temperatures.

Antioxidants, as defined by Food and Drug Administration are “substances used to preserve food by retarding deterioration, rancidity or discoloration due to oxidation.” Some oxidations have more than one function. For example, Ascorbic acids may function as a free-radical chain terminator, and oxygen scavenger, or a metal chelator. Under certain conditions, it may act as a promoter for oxidation.
Vitamins as antioxidants in processed foods