Potatoes should be harvested at full maturity when they have attained a high level of dry matter and low reducing sugars [9] [10] . Physiologically mature potato tubers are not easily injured during handling and transportation. Due to financial pressure, most potato farmers in Kenya are forced to harvest immature tubers which are sold immediately to obtain cash income [11] . This means most of the tubers have high reducing sugars, a major factor in acrylamide formation during frying.

Harvested tubers should be cured at high temperature and humidity (12˚C - 25˚C/85% - 95% RH) to facilitate healing of wounds incurred during harvesting. The operation also helps the wet tubers to dry off. Unlike large scale processors who have organized stores, most small scale processors who make up at least 80% purchase raw tubers from open air markets which sell immature and non-cured tubers [5] . In most cases potatoes are harvested and taken to the market immediately. Poor potato packaging and handling of large bags above the legal limit of 110 kg and exposure of potatoes to sunlight which is common in Kenyan markets are practices which greatly increase the risk of exposure to glycoalkaloids [12] [13] . High chances of buying greened immature tubers and hence accumulated glycoalkaloids is very likely in the local cultivars [14] . Raw material selection by a few large scale processors is done on the basis of size, reducing sugars and specific gravity while small processors who have no means of ascertaining these parameters select tubers visually based on tuber size and color preference, whether red or white skinned [5] .

Sorting plays a critical role by removing very thin slices or sticks which easily burn off and make the frying oil dirty facilitating quality degradation. It is also a process meant to remove defective and greened pieces. Sorting in large processing set-ups is carried out immediately after frying to remove either greened or dark brown slices

of crisps. It is, however, rarely carried out in the street and cafeteria processing. It is therefore common to find many greened and dark brown pieces of fries or crisps in the final product [5] . Dark brown colored crisps are often masked by application of colorants. This may be an avenue of exposing consumers to high levels of glycoalkaloids and acrylamide.

Washing is usually done to remove excess starch that is exposed due to rupture of potato tuber tissues in order to avoid making the frying oil dirty and reduce the rate of breakdown. Blanching either in water or oil ensures light colored fried products following extraction of reducing sugars and asparagine which are known to interact to produce acrylamide [10] . For most small scale processors, washing takes very short time and blanching is not common and hence the increased probability of producing high acrylamide fries. On the other hand, medium and large scale producers have to hold the chipped or sliced raw potatoes for longer duration before frying and hence employ the use of anti-browning agents such as sodium metabisulfite instead of blanching which is considered as an added cost. The use of sulfur dioxide is gaining momentum especially due to increased production and sale of “fresh cut” French fries which are prepared by chipping, soaking in sulfur containing water, draining and packaging. Indiscriminate use of this chemical in processing plants can be a health hazard.

Frying of potato crisps and French fries in Kenya is carried out under varied conditions with limited controls. Large scale crisps processors and most medium to large hotels who sell fries have adequate temperature controlled equipment which is lacking among small processors, chips (French fries) joints and street food dealers makers who make up a sizable proportion. Use of higher than necessary and unregulated temperatures for frying is therefore not uncommon; this may lead to extremely high levels of acrylamide in the final product given the fact that the tubers used could be high in reducing sugars as well. Almost all crisps producers use liquid oil for frying, generally palm oil based [5] [15] . On the other hand, majority of French fries producers use solid fats which are either hydrogenated or non-hydrogenated. Interestingly, replacement of frying oils is quite dependent on the set-up; most (70%) establishments replace oil daily, while other set-ups (27%) can use the same oil continuously for about 2 - 4 days (authors unpublished data). Although the majority of processors discard spent oil, a good number use it for frying other snacks such as ground nuts, doughnuts and sausages [5] . Chances of producing fried products with high levels of polycyclic triacylglycerides and trans fatty acids is therefore highly likely.

Different flavors and colorants are applied to fried potato products after frying mainly to enhance their palatability and taste. A number of flavored crisps exist in Kenyan retail market ranging from plain salted, cheese and onion, tomato and so on [5] . The type and amounts of these flavors depend on the producer especially in cases where street products are concerned. Customers may therefore be consuming higher than recommended amounts coupled with the fact that their microbial diversity and loads are not known. French fries are normally served immediately after frying in many set-ups and the consumer adds at will the diluted tomato and hot (chilli) sauces whose hygiene standards are not ascertained.

Potato crisps are mainly packaged in polyethylene plastic bags which vary in make and thickness, while a few brands are packaged in aluminium packs. On the other hand, the hot-served French fries are packaged in polyethylene bags and different types of paper including plain paper. Studies on migration of packaging materials into these products have not been carried out in Kenya, but this may be a potential hazard.

The glycoalkaloids in potatoes are natural toxic substances with alpha-solanine and alpha-chaconine being the most predominant [25] . Solanine content varies with potato variety since it is genetically controlled; values in European and United States have been reported to range from 2 to 15 mg per kg of unpeeled tubers [26] . However, regional and geographical conditions influence the levels of glycoalkaloids. Injuries during harvesting and poor post-harvest handling practices such as exposing potato tubers to sunlight increase the levels of glykoalkaloids with high concentration in the skin [27] . It is generally agreed that the best raw potato for processing should not have more than 20 mg total glycoalkaloids (TGA) in 100 g of tuber [28] . Higher levels beyond 100 mg/kg are potentially dangerous; some countries have even set the upper limit to be 10 mg/100 g sample [29] . Susceptibility of humans to side effects of glycoalkaloids has been shown to be very high and varies from person to person [30] . It has been shown that an oral daily intake of 1 - 5 mg/kg body weight can have marginal or severe toxic effects to humans [31] . Consumption of high levels of glycoalkaloids has been associated with negative health effects such as gastrointestinal discomfort, vomiting, fever, diarrhea and neurological problems and can lead to human or animal deaths in cases of acute toxicity [32] [33] . Glycoalkaloids are normally heat stable and hence only limited reduction may be achieved during processing and it becomes even more difficult when tubers have high accummulations [34] [35] . Large scale glycoalkaloid poisoning is rare though mild poisoning is suspected to be more prevalent than many can imagine [36] . Difficulty in diagnosis of poisoning is compounded by the fact that symptoms of toxicity are similar to other gastrointestinal disorders [37] .

The toxic action of Glycoalkaloids may be two folds. First, it may affect the cell membrane by disrupting the phosphatidylcholine or cholesterol liposomes at higher concentrations of 50 µMol [38] . Glycoalkaloids have been shown in animal studies to negatively affect intestinal permeability and long term exposure could lead to chronic inflammatory disease of the bowel [39] [40] . Secondly, it can also act to inhibit acetylcholinesterase both in humans and bovine especially at higher levels of 100 µMol [41] . Both chronic and acute toxicity of glycoalkaloids are possible [42] .

In a study conducted by Kirui et al. [14] to quantify levels of total glycoalkaloids selected Kenyan varieties and advanced clones, the levels were found to range from 3.5 to 17.5 mg/100 g, which was in the normal range of less than 20 mg/100g. Results from other researchers in different countries are given in Table 1. These results of Kirui et al. [14] were, however, obtained by analyzing tubers under well controlled field experimentation and storage at the National Potato Research Centre, potential risk of glycoalkaliod toxicity may be high due to increased consumption of potato and potato products, some of which are transported or handled poorly. Poisoning of animals that are fed greened tubers and peels remain to be assessed.

¹Low and high ranges from literature.

Deep fat frying is generally adopted as a fast and convenient way of producing foods acceptable to large number of consumers. Oil used during food preparation determines the food flavor, stability, texture and taste. There are, however, several concerns that have been raised regarding deep fat fried foods. Firstly, the amount of oil absorbed by frequently consumed foods such as potato crisps and French fries has been a major point of debate since the oil absorbed during processing becomes part of the diet [6] [44] . Many nutritionists have blamed these high energy food products as major causes of obesity [45] and cardiovascular disease [46] [47] . A number of potato crisps brands in Kenyan market, for instance, were found to have higher than the recommended East African Standards maximum limit of 35% oil content [5] [19] .

Secondly, it is a well-established fact that some compounds formed during frying potentially toxic which are responsible for physical and chemical changes in frying oil pose great danger to human health [48] . Due to high temperatures normally used, break down of frying oil leads to formation of dangerous compounds such as polymerized triacylglycerol, trans fatty acids, conjugated dienes and oxidation products [45] [49] . High levels of phytosterol oxidation products (POPs) have been detected in French fries samples from restaurant being related to higher contents of fat, saturated and monounsaturated fatty acids and sterols [50] . POPs and other sterol epoxides formed during frying depend on frying temperature, fatty acid composition and phytosterol contents of individual oil used in frying and have been found to be high in some restaurants as well as French fries also in Sweden which may pose risk to consumers [51] [52] . Such studies are yet to be carried out in Kenya to ascertain the extent of their occurrence especially when frying oils are abused. Observation of proper frying time or turnover is critical to ensure safety of fried products.

For sometimes now risks due to abuse or extensive and indiscriminate use of food additives have become major food safety concerns [53] . The risks arising from food additives are considered invisible and may be seen as a violation of consumer safety rights [54] . Major groups of food additives extensively used in foods include preservatives, color, flavor enhancers, and spices. Exposure of sulfite to Kenyan consumers remains unknown due to lack of adequate evaluation and control systems. However, sulfite has been associated with negative health effects especially for ready to eat foods since it causes asthmatic reactions and may also affect the nervous system in some individuals [55] [56] . Different flavor enhancers and colors are also used in French fries and potato crisps some of which may be harmful when indiscriminately used [57] [58] . The actual level of exposure remains unknown due to lack of evaluation.

Microbial contamination of sauces and salads used in restaurants serving French fries has been reported in other parts of the world. Contamination from Escherichia coli, Staphylococcus aureus, Bacillus cereus, Salmonella and other pathogens known to cause serious illnesses have been reported in the United Kingdom [59] . Fungal and bacterial contamination of herbs has also been reported in other parts of the world [60] . In light of unregulated street food preparation some of which are unhygienic, likelihood of contamination of sauces and fries is high [61] . Since these sauces are consumed directly without further heating, their impact on human health can be deleterious.

Discovery of acrylamide in fried products has raised serious food safety concerns the world over [62] . Acrylamide is a chemical that remains a suspect human carcinogen and a neurotoxicant with adverse effects on normal metabolism [63] [64] . Depending on the amount and type of food being consumed by an individual, carcinogenic and genotoxic risks due to acrylamide in the diet vary considerably [65] . High levels of acrylamide up to 4565 ppm have been reported in Kenyan potato crisps [66] . The current high values are beyond the indicative value of 1000 ppm given for other countries and regulatory bodies such as the European Food Safety Authority [67] and other researchers worldwide (Table 2). Surveys carried out in many parts of the world indicate higher exposure of acrylamide especially from French fries and potato crisps. Total diet study in France, for instance, indicated lower exposure margins for children [24] . Exposure to acrylamide via fried potato products have been reported in Belgium [68] , Italy [69] and Norwegian population [70] . Due to high consumption of the fried potato products in Kenya, mainly the urban dwellers, exposure to acrylamide could be high and so is the likelihood of contribution to negative health effects. Proper mitigation measures would involve capacity building along the chain from production and harvesting practices to storage and processing.

Studies on migration of packaging material components into foods have not been carried out in Kenya, but it remains a potential hazard. Chemical migrants, however, will depend on the type and amount of food, temperature and molecular size of the chemical in packaging material [77] [78] . The negative effects of these migrants to food safety can no longer be over looked if safety of the food supply is to be assured [79] . Chemical migrants from polyethylene in both simulants and true foods have been reported in Europe, being high in oily foods under higher temperature [80] [81] . Similar trends have been reported in Brazil [82] . Since French fries are packaged in polyethylene and papers while hot, risks of consuming high levels of migrants cannot be overemphasized.