Introduction

The production and  consumption of coffee has been increasing over the last half a century ¹.  The current consumption patterns are attributable to increased disposable incomes among the middle class earners, improved coffee qualities, and decreasing retail prices¹. Data from FAOSTAT indicates that more than 70 countries across the world are now producing the crop characterized by considerably high number of small-scale farmers. Some coffee producing countries have seen considerable benefits through higher yields and growing volumes of sales. The coffee sector is however faced with increasing challenges as a result of the climate change and diminishing natural growing conditions and environments. The crop is mainly cultivated as a cash crop and has seen tremendous growth in the international trade estimated at over $19 billion since 2017².

Coffee is usually traded in large quantities with different varieties, forms i.e. processed or raw, quality of the beans and the source of procurement fetching different prices ³ . The two broadly traded varieties are Arabica and Robusta, and are usually sold in roasted or green conditions, while in processed forms, this may be either instant or in soluble form ¹. In most developing countries, coffee is an export crop and has been a major source of valuable foreign exchange ⁴ .

In Kenya coffee farming supports many smallholder whose livelihoods depend on the crops’ cultivation ⁵. Although Arabica and Robusta were the two major varieties grown in Kenya, about four cultivars that adapt to both high and low altitudes have been developed from the Arabica variety with Ruiru II variety bring a common clone.  The crop thrives well in attitudes of 1 400 to 2 000 meters above sea. Coffee farming is however on the decline due to reliant on many small scale farmers who have been faced with constraints including high production costs, and lack of incentives besides the low economic returns from the cooperatives managing the coffee farmers despite the international market demands for Kenyan coffee ⁴ (Figure 1).

Figure 1: Coffee production trends, 1994-2018 showing the declining  coffee cultivation and production according FAOSTAT.6 Click here to view Figure

The Kenyan coffee farming is coordinated by the ministry of agriculture promotes an agricultural sector of Coffee Directorate through Agriculture and Food authority to ensure efficiency in production and postharvest handling ⁷. Produced coffee undergoes primary wet, dry processing and grading at the local production sites, often characterized by farmer’s cooperative societies and thereafter transported to private service providers and processors for further processing ⁸. Although coffee consumption been shown to have various health boosting effects on consumers including lessened risk for heart diseases, cancer, and liver diseases besides the various phytonutrients from the beans among others ^9,10, it faces stiff competition from tea consumption which is the most preferred beverage nationally due to low consumer purchasing powers for the imported coffee which are predominant in the local markets. This is however changing as a result of increasing middle income earners and increased coffee houses and malls ⁸.

Although the consumption of coffee has been on the increase in the past few years ^8,11, there have been concerns on the safety of the beverage due to the presence of acrylamides which occur in roasted beans during processing of coffee ^12–14. There are however, limited studies on the levels and presence of acrylamides in marketed coffee within the Kenyan markets. The current review discusses acrylamides occurrence in processed coffee and the potential safety concerns due to intake of acrylamides through processed coffee consumption based on findings from a comprehensive literature review.

Occurrence of acrylamides in Foods

Acrylamides commonly occurs in roasted or baked foods ^15,16. The high processing temperatures and the presence of free amino acids and reducing sugars facilitate the occurrence of these toxicants in the processed foods ¹⁴. Given the potential of acrylamides to cause adverse neurotoxic and carcinogenic effects, there is need to ensure that their levels in foods are within safe levels especially for foods that involve high temperature cooking during food preparation including baking, roasting and frying, among others ¹⁶.  There is paucity of information on the presence of acrylamides in coffee and there is no data on acrylamide poisoning in the country despite studies showing that they cause widespread human risk exposure ¹⁷

Acrylamides are potential toxicants formed by Maillard reactions at cooking temperatures exceeding 120^oC through the reactions of free asparagine, an amino acid and reducing sugars in foods ¹⁸. Acrylamides were first reported by the  Swedish National Food Agency in 2002 and the United States of America’s food and drug authority (FDA) according to Vattem & Shetty¹⁹. Since then, various studies have shown that acrylamide exposure through contaminated foods have potential to cause neurotoxic and carcinogenic effects among animal studies ^20,21 with human beings being at a high risk of experiencing carcinogenicity ²² besides other health threating conditions.

Studies by Lingnert and colleagues ²³have reported that the toxicants mainly occur in plant-based foods, such as potatoes, cereals products, as well as in coffee during the long time and high temperatures cooking combinations. Acrylamides however, are less prone in animal-based foods, such as meat, and fish, among other products, because it only occurs in the presence of reducing sugars which may be absent from animal based foods ^12,18. The presence of acrylamides in foods have however, not been found to be influenced by either the food packaging materials or the environmental conditions but majorly through the Maillard  reactions which are complex reactions that occur as a result of amino acids and sugars interactions under high temperature ²⁴. Foods including fried potatoes such as crisps and French fries and baked cereals and legumes have been found to contain various levels of acrylamides ^12,25 with indicative safety limits set at varying concentrations ²⁶ (Table 1). Acrylamides are also water soluble and have been detected in drinking water exposing the consumers to food safety risks ^27,28 . In coffee beverages, they diffuse through into the consumers’ drink at different levels depending on the surface area to volume ratio of the beans used ¹⁴.In Kenya, limited studies on the occurrence of acrylamides have been conducted, mainly on potato crisps and French fries^29,30although most foods with potential to accumulate the toxicants remain under studied.

Table 1: Indicative values for acrylamide levels in foods.

Adopted from ²⁶

The occurrence of Acrylamides in Coffee

Coffee  is now one of the most consumed beverage across the world and is probably the major drink through which consumers are exposed to acrylamide intoxication ¹⁸. Kenya’s altitude, rainfall, volcanic soils, and temperature enhance coffee farming ³¹ and consumption among Kenyans and foreign visitors has seen a tremendous growth since the last decade ^8,31 given the increasing disposable income and luxury associated with coffee drinking.

Acrylamide are heat-caused food toxicants formed through the Maillard reaction between asparagine and reducing sugars when processing food ³². The levels of acrylamides in coffee are influenced by the degree of roasting, the coffee variety under processing, and the conditions of storage ^32,33 . Various ways of coffee brew preparation, depending on regional and personal tastes, may result in distinct amounts of acrylamide in coffee brews and, consequently, to different vulnerability to this compound.³²

Different coffee products have been shown to accumulate varying levels of acrylamides as reported by Mojska & Gielecińska¹⁸. Out on 42 coffee samples, composed of 11 instant coffees and three coffee substitutes (grain coffee), the study found that instant coffee had 100% more acrylamide than freshly roasted coffee, while coffee substitutes had 300% more acrylamides. Furthermore, the study also noted that acrylamide levels increased early during the heating process and then reduced as the processing continued. Similar studies have also supported similar findings and it has been shown that lighter colored coffee beans have more acrylamides compared to the darker coffee beans roasted for more extended periods ³⁴.

Health effects of acrylamide intake

Acrylamides have been shown to be  potential risk factor for cancer, according to Wachamo, (2017)⁹. The chemicals are dangerous at higher levels, but cannot be removed from coffee once the processing is completed, although many studies suggest that coffee consumption relatively increases the risk of cancer occurrence. ¹⁶ Acrylamides are also potential triggers free radicals production among the white blood cells leading to likelihood of diseases as well asinducing inflammation and oxidative stresses responsible for atherosclerosis among frequent consumers of coffee.³⁵

Although the recommended safety intake margins for acrylamides have  been  set at 1-4 µg/kg/bw according to the WHO/FAO-JECFA³⁶, there haven’t been well established recommended limits given that there have been limited studies on the acrylamides kinetics and behavior in human bodies to make scientific conclusions. The  FAO/WHO, (2010) Joint Expert Committee on Food Additives reports that the toxic nature of acrylamides occurs from the fact that the toxicant is converted into reactive epoxy compound within the body and these form a basis for intoxication. Consequently, the higher the levels of consumption, the higher the toxicity among consumers. Exposure to acrylamides intake of by animals and human beings increases the risk of cancer development more so when where the exposure is in high dosages³⁸. Therefore,  there is a need for more investigations to determine the implications it causes in human health ¹⁷.

High levels of acrylamide in coffee through roasting poses significant  health problems among children and adults ³⁹ with children and younger generations being at higher risks given their relatively lower body weights. Besides neurotoxicity and carcinogenicity, other condition have been attributed to the toxicants especially in in younger generations ¹⁵ including inadequate responses, sparse learning insufficient brain chemicals that help in signal transformation and loss of body weight. Excess acrylamide levels cause nervous system problems including numbness, muscle weakness, sweating, clumsiness, and unsteadiness ⁴⁰. High levels of acrylamide chemicals has been found to promote decreased ability of males to create offspring ⁴⁰ among laboratory test animals.

The use of coffee has been demonstrated to have potential long-term effects since the levels may be low in coffee. Besides, processed coffee has low acrylamide levels; hence it cannot cause the health effects in the short-term, as suggested by ³⁹.  However, there are other factors which determine whether one is affected upon exposure to acrylamide or not. These factors include duration, dosage, way of contact, state of heath during exposure among others ¹⁸ The effects of acrylamide  in human bodies have however had conflicting reports as potential precursors responsible for many cancer cases in animals studies, though there is no adequate epidemiological studies to support this especially among human beings as studies have shown potential contribution to cancer occurrence among consumers.^41–43 Therefore, the actual number of consumers exposed to acrylamides risk of exposure in Kenya remains unknown.

Consumer exposure to acrylamide

Exposure to acrylamides occurs through oral via consumption of contaminated processed foods and water, dermal route through industrial acrylamides and polyacrylamides and gaseous inhalation through smoking of tobacco ^12,28. The dietary exposure has however been found to contribute to relatively higher levels subject to the contamination levels , estimated to be up to 39% among the high coffee consumers.⁴¹The various processing parameters for potential foods has also been shown to vary according to USDA resulting to varying levels in the finished products.

The dietary exposure to acrylamides through heat processed foods has continued to raise a worldwide concern as the contaminants easily diffuses into the body tissues including the placenta and into the fetus. They further distribute into the body fluids through accumulation in the body has not been well documented. Assessing acrylamide risks depends on the levels of food substances intake that contain the chemical⁴⁴. Those exposed to higher levels of foods and substances containing Acrylamide are likely to show health effects that could help determine the risks. For instance, Acrylamide in coffee relatively increases the risk of getting cancer across every age group. Acrylamide gets into the body organs through absorption and results to acrylamides metabolism. This metabolism causes gene mutation, tumors development, and other gland defects in animals.

Acrylamide is also responsible dangerous effects on other body systems like the nervous system and studies have also shown a likelihood of paralysis and infertility among males in animal trials dosed with different levels of the chemical⁴². Human studies have given limited evidence on the risk of cancer development in the liver and kidney. Acrylamide is found in coffee and other everyday foodstuffs, children get the most exposure, enhancing risk assessment in terms of body weight losses²⁶. Storage of food, ingredients, and conditions involved during processing influence acrylamide accumulation food⁴⁵. Diet routines, home-cooking, and other choices by different homesteads would help us assess the risks. Health checkups will effectively help to show those affected in terms of exposure to acrylamide levels⁴⁵.

According to Barlow⁴⁶, the margin of exposure (MOE) approach indicates the degree of health concern about the presence of a particular component in food without quantifying the risk. The MOE’s use helps risk managers recognize the necessary decisions needed to keep exposure to such substances at low levels possible. For carcinogenic and genotoxic substances, a MOE of higher than 10,000 is of moderate concern to the public health. In Kenya, evaluation of acrylamide exposure through French fries and crisps consumption was ranged from 0·3–0·8 µg/kg body weight per day established on exposure calculations made by FAO/WHO⁴⁶ . Acrylamide exposure was at an average of 1 µg/kg body weight a day as the highest exposure in adults was almost 0·5 µg/kg body weight in a day, with 95th percentile figures of practically 1 µg/kg body weight per day. Exposure is high among younger Kenyan people between the age of 15-18 years, as the 95th percentile was 3·4 µg/kg body weight per day.⁴⁷Similar studies on coffee remain absent and there is need for conducting such studies. However, limited dose response studies are still recommended for adequate evaluation of the intake consequences.

The acrylamides concerns across the world raised consumer safety concerns leading to the WHO/FAO to conduct adequate assessments for exposure through food ⁴⁸. However, there have been limited doxological data leading to limited information on the probably consequences from their exposure ⁴⁸. Furthermore, there is likelihood that low doses in commonly consumed foods among consumers whose potential harm may still be unknown. This therefore requires increased risk assessment to assess the consumption of varying levels of the effects on consumers’ health.

Effect of different processing parameters on acrylamide levels in coffee

The occurrence of acrylamides in uncooked raw foods have not been reported and these occur strictly through processing through the Maillard reaction ^12,48. Asparagine has been reported to be the main precursor for the formation of acrylamides ⁴⁹ and forms significant quantities at elevated temperatures similar to thermal processing. The levels have however been found to increase more than 12 fold in the presence of reducing sugars ^18,49,50.

Other processing parameter such as pH, processing temperature, presence of ocrolein and ammonia among others during processing have been reported to be catalysts for accumulation of acrylamides in processed foods ⁵¹. However, data from most developing countries remain undocumented and in Kenya, this also the case. The occurrence of acrylamides, quantification of their levels, formation in processed foods, as well as exposure among different age categories have been widely studied across different countries, though limited epidemiological studies have reported differing information on cancer disease formation among consumers ⁴⁸. There are no enough such studies in Kenya therefore limiting reporting of the occurrence and potential food safety and health concerns for consumers.

Mitigation of acrylamide in processed coffee products

The levels of acrylamides are highly dependent on the selection of cultivars for processing, the roasting conditions, storage and the brewing processes (Figure 2).Based on the indicated probable consequences of acrylamide, there is an increased need to create rational solutions ⁵². Among the various ways of reducing the amount of acrylamide ingested in beverages include; deep roasting of the coffee beans to darker conditions using darker temperatures ranging from 220^oC to 250^oC considering both the speed and time (20-30 minutes) of roasting, because these conditions contribute to the taste and aroma as suggested  by.⁵² This is because at higher temperatures, the acrylamides are broken down and therefore less accumulation. Consequently, lightly roasted coffee beans have far much less acrylamides ⁴².

Coffee to be processed should be properly selected from desirable raw material (green and quality coffee beans) since varietal effect in the levels of acrylamide have been found to have a significant effect. Studies have shown that the two dominant coffee species Arabica and Robusta, are differentiated by sensorial possessions and chemical configuration where Robusta coffee species have higher acrylamide content compared to Arabica⁵³. The amount of the ultimate contents of acrylamide depends on the various processing conditions involved.⁵² Therefore, it is recommended that it be blended with higher amounts of Arabica coffee species to reduce the levels of acrylamides.  The storage periods should also be longer because acrylamides are usually unstable during the roasted coffee packaging, as indicated by Figure 2. To reduce the amount of acrylamide in coffee, the products should be stored at room temperatures in closed vacuum packs for 12 months.⁵² It is also necessary to prefer shorter brewed coffee over longer ones., which proved to be the best brewing method compared to the other ways. During consumption preparation should also involve a short infusion period for freshly prepared coffee beverage. ⁵²

Other techniques, such as reducing the key reactants, such as fructose and glucose, and the responsible amino acid, asparagine, prior to the high-temperature heating process by disrupting their reactions with the addition of other amino acids and food-grade acids, can alter the reaction conditions and thereby prevent high accumulation.³⁵ Moreover, soaking bans may reduce sugar accumulation because the sugars will dissolve in the soaking water, and avoiding temperatures above 190^oC is advised.⁵⁴

Figure 2: Processing of coffee showing critical points during coffee processing with the red highlighting critical processing steps. Click here to view Figure

Methods of determining acrylamides in foods

Several methods have been developed though none has been conventionally agreed on for their reliability in rapid detection and sensitivity.⁴⁸ Consequently, there has not been a standardized method and there are new methodologies being developed to date. Significant methods for analyzing presence of acrylamide in the foods are liquid chromatography with mass spectrometry, LC-MS (/MS), and Gas chromatography with mass spectrometry, GC-MS (/MS).¹² Liquid chromatography a standard technique used in analytical food chemistry for ascertaining the existence of organic trace compounds in food analysis. It uses the resolving power of liquid chromatography together with the detection specificity of mass spectrometry. LC involves the separation of sample components and presenting them on to the mass spectrometer (MS). The MS forms and distinguishes charged ions.

On the other hand, GC-MS (/MS) works on the principle that the sample separates into independent substances when heated. The method uses heated gases which go through a column filled with inert gas, for example, helium. The sample isolated comes out through the column opening as they flow to the MS.²⁹  For accurate results, analysts prepare food samples through a solid-phase extraction method before analysis by chromatography⁵⁵. This extraction method is essential as it optimizes the example, besides, it reduces background contaminates and may even concentrate the compounds of interest. Analytical instruments used for the quantification and detection of acrylamide include Nitrogen phosphorus detection (NPD), gas chromatography (GC); coupled with electron capture detection (ECD), flame ionization detection (FID), liquid chromatography (LC); coupled with ultraviolet detection (UV), fluorescence detection, or, flame photometric detection (FPD).

Although the various methods have been tested in other studies, in Kenya, there is limited information on the most reliable detection methods and the limited studies have majorly been reliant on high pressure liquid chromatography (HPLC) analysis for potato crisps and French fries. ^47,56 It is recommended that other methodologies be assessed and the scope be increased so as to cover other acrylamide accumulating foods such as cereals based baked foods.

Conclusion

Despite urinary excretion, acrylamide is rapidly absorbed and widely distributed throughout the body. Studies have revealed that acrylamide has reproductive, genotoxic, and carcinogenic effects; therefore, it is imperative that consumers consume as little of these contaminants as possible, given the possibility of adverse effects on their nervous systems. Given Kenyan coffee consumers’ limited understanding of acrylamide intoxication and their estimated intake levels from locally processed and ground coffee, there is a need to raise awareness about the safety and potential poisoning associated with coffee consumption if contaminants exceed the recommended safe levels. There are also no known levels of acrylamide accumulation in locally processed and ground coffee, necessitating further research on the topic and the adoption of standardized methods for processing coffee with low acrylamide levels by processors.

Acknowledgement

First and foremost, I appreciate the Almighty God for granting me good health and wisdom during the entire study period. A special thanks and recognition goes to my supervisors Prof. Micheal Okoth and Dr. George Abong’s  for their professional guidance and encouragement during my study period and Dr Mbithi Boniface for his assistance with data analysis process. I also wish to express appreciations to the whole department of Food Science and Technology for their immense contributions during my study period.

My sincere gratitude goes to local administration Nairobi City County, the respondents and enumerators for their cooperation during the data collection process.

I would like to gratefully and sincerely thank my lovely wife, Mulki Abdullahi, my sons and daughters Abdulqafar, Abdullahi, Hanifa,Abdulrahman and Haifa, my parent and my siblings for their understanding, patience and most importantly their friendship during my research period and thier continuous encouragement and contributions towards the success of my studies.

Conflict of interest

Authors have no conflict of interests.

Funding Sources

This work did not receive any funding.

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