Food is an organic substance once eaten provides human body with the required energy. Food is mostly organic in that it contains carbon and hydrogen molecules and degenerates over time. Food once exposed to air undergoes reaction which is normally referred to as degeneration. Scientists have observed that, if left unattended, food provides a perfect breeding site for micro-organisms. These micro-organisms which include bacteria and fungi produce poisons as they multiply while feeding on the food. This, if consumed can lead to fatal cases of diarhoea and food poisoning.
It is due to this degeneration that people have come up with means of food preservation to make sure it last longer. Food preservation involves the delaying of the onset of multiplication of these micro-organisms. Food preservation is a process by which are prevented from getting spoilt for a long period of time. The colour, taste and nutritive value of the food are also preserved. (The National Institute of Open Schooling (NIOS))
People over time have leant on better ways of keeping their food safe. The historical perspective of food preservation can be traced back to the early human development. When humans were hunters and gatherers, there was no need to preserve any food and early human could gather what they needed for the day. However, with the onset of agricultural production, farmers were faced with a challenge of making sure the harvest lasts until the next and they had to devise a way of preserving food. Early methods of preserving food were by smoking and drying. Later on they discovered salt and used it for preservation. Over time, the methods have improved to the modern ones including food additives and refrigeration.
A story is told of how humans observed insects and the manner in which they were working during the sunny day and keeping enough stock for the rainy days. This concept has been adopted as the driving force behind food preservation.
There are various reasons why foods are preserved. The basic one is that people will need to keep some food to use when the supply is low. For example, people in Kenya do not have access to certain fruits all through out the year. To avoid a situation when they need that sweet mango and they can not find it anywhere, people opt to either process it into a fruit juice or manufacturers put it in can and use it later. This provides an opportunity where people have access to certain foods through out the year. The case is same in countries where they experience four seasons like US and Europe. Certain crops do not do well in winter hence the need to keep good stock.
Another reason for food preservation is that many people are aware of the need to avoid food wastage. Excess food is stored and used when there is less supply. People buy refrigerators so that they can keep the excess food and eat it later. As we will look later on in this paper, long periods of food in refrigerators can also be dangerous.
To help us understand how food poisoning works, we need to understand the nature of micro-organisms and how they relate to human body.
The human body is a well organized system allowing in beneficial micro-organisms and fighting those not beneficial. It is equipped with several defensive mechanisms including the skin, body fluids and gut enzymes that keep the body free from attacks. The body’s defense systems detect micro-organisms and determine if they are pathogenic or virulence. This means they are capable of causing diseases.
Pathogens on the other hand have evolved long enough to devise their adaptation and trickery to dupe the body’s defense mechanisms. For example micro organisms overwhelm the body cells by quickly multiplying and infecting the body before it realizes (Forbes et al). They also attack cells involved in defense.
Micro organisms produce poisons to help them establish infections and multiply within the host. For them to do this, they require toxins that in most cases cause disease in absence of pathogens.
Medical dictionary (http://medical-dictionary.thefreedictionary.com) defines food poisoning is a general term for health problems arising from eating contaminated food. Food may be contaminated by bacteria, viruses, environmental toxins, or toxins present within the food itself, such as the poisons in some mushrooms or certain seafood. Symptoms of food poisoning usually involve nausea, vomiting and/or diarrhea. Some food-borne toxins can affect the nervous system.
staphylococcus aureus is found on humans and in the environment in dust, air, and sewage. The bacteria is spread primarily by food handlers using poor sanitary practices. Almost any food can be contaminated, but salad dressings, milk products, cream pastries, and any food kept at room temperature, rather than hot or cold are likely candidates. (Gladwin
Human Skin Pigmentation Processes
Human skin pigmentation can be regulated by various physiological factors such as hormones, peptides derived from pro-opiomelanocortin (POMC) and also by the -melanocyte-stimulating hormone (-MSH) via the melanocortin-1-receptor (MC-1R) pathway. A further factor believed to have a regulatory mechanism in human skin pigmentation is a key enzyme known as tyrosinase.
Melanocytes also have a role in determining and regulating the human skin pigmentation. Melanocytes form two types of melanin these are eumelanin and pheomelanin. The amounts of these two types present determine the colour of the hair and skin. For those who have mostly eumelanin have will have darker skin. Eumelanin also is very important as it is important in helping protect the skin against damage that is caused by UV radiation. Whereas pheomelanin does not protect against UV radiation so those people with more pheomelanin are in risk from damage to the skin by UV radiation. Also those with more pheomelanin tend to have lighter skin.
The type of melanin that is produced by the melanocytes is controlled by the MC-1R. The MC-1R is a receptor which can be found on the surface of the melanocytes which are specialised cells which produce melanin via a process known as melanogenesis. This is a G coupled protein which binds to melanocortin peptides such as ACTH and a-MSH and is involved in regulating human skin pigmentation.
Each of these factors affects human skin pigmentation in different ways.
The human skin is thought to be a local source and a target for POMC The many peptides that are derived from POMC such as (-MSH) and adrenocorticotropic (ACTH) as well as POMC itself which are believed to have an important role in the regulation, and control of human skin pigmentation, by acting on the melanocortin-1 receptor (MC-1R) and also regulation of the melanocytes. These peptides and hormones are produced via the enzyme known as prohormone convertases (PCs) which cleave the POMC at different points. Different POMC derived peptides produced act on specific melanocortin receptors this is dependant on the tissue.
POMC is involved in the stimulation and increase in melanogenesis and the dendricity in human pigment cells. Mutations of the POMC genes in patient s have lead to pale skin and other problems such as red hair and obesity. This change in the hair colour and pale skin is believed to be because there is a lack of ligands for MC-1R (kligman AM 1959, Krude H et al). Also MC-1R polymorphisms are also thought to cause pale skin because they reduce the MC-1R activity. Administration of ACTH and -MSH to humans has shown a significant darkening of the skin. If the ACTH is administrated for a prolonged period of time this can lead to hyperpigmentation. Excessive concentrations of POMC can be detected in adission’s and nelson’s syndrome which can also lead to hyperpigmentation. POMC peptides are thought to cause stimulation of melanocyte tyrosinase and melanogenesis. Finally at high concentrations POMC can lead to an increase in melanin and the further effect is to help increase the dendricity of human epidermal melanocytes.
A further regulator of human skin pigmentation could be Β-endorphin (Β-end). There are several observations which have stated that (Β-end) may have a role in regulating human skin pigmentation. Studies have shown that after UVA exposure there is an increase in (Β-end) which has been associated with the pigmentation of the skin increasing (levins et al, 1983; Belon, 1985). However it has been recently discovered that exposure to UVA, UVA-1 OR UVB radiation weather once or repeatedly does not lead to an increase in the levels of Β-end in the plasma (Wintzen et al, 2001).
The precursor of Β-end which is Β-lipotropic hormone (Β-LPH) is said to stimulate melanogenesis in amphibians and in sheep (Lohmar and Li, 1968). High levels of Β-LPH have been generalised with humans having hyperpigmentation. Research has found that the Β-END/µ-opiate receptor system is important in regulating melanocytes because of its ability to up regulate melanocyte dendricity, proliferation and also pigmentation.
Β-end acts opposite to ACTH and a-MSH which stimulate melanogenesis by acting on the MC-1R and activate cAMP messenger system (Busca and Ballotti, 2000). The Β -END works by inhibiting this signalling pathway. Research has proposed that the Β-end/µ opiate receptor may be acting via the protein kinase C inhibitor which causes the tyrosinase to be activated directly and also stimulates melanogenesis.
Β-end has a role in human skin pigmentation however the mechanism is different from other peptides such as ACTH and a-MSH because Β-end mechanism is independent of the MC-1R which is used by the ACTH and a-MSH. Β-end is a potent modifier of melanocyte phenotype this is achieved by upregulating melanocyte dendricity, proliferation and melanogenesis.
To conclude there are many different methods of regulating human skin pigmentation and also different pathways via which different hormones and peptides affect human skin pigmentation. One of the major regulators in human skin pigmentation are peptides derived from POMC such as ACTH and a-MSH which are stimulated by the MC-1R pathway and also involves the cAMP messenger system. Research has shown that there are a combination of factors mostly internal factors which regulate human skin pigmentation however there is some evidence that external factors such as UV radiation can also cause changes in the regulation of human skin pigmentation.