Journal of the Science of Food and Agriculture J Sci Food Agric 85:2595–2599 (2005) DOI: 10.1002/jsfa.2313

The effect of delayed harvest on moisture content, insect damage, moulds and aflatoxin contamination of maize in district of Archileo N Kaaya,1∗ Herman L Warren,2 Samuel Kyamanywa3 and William Kyamuhangire1 1Department of Food Science and Technology, Makerere University, PO Box 7062, , Uganda 2Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24061, USA 3Department of Crop Science, Makerere University, PO Box 7062, Kampala, Uganda

Abstract: Field drying is a traditional practice carried out by farmers in Uganda and it is one of those practices reported to affect the postharvest quality of maize. A study was therefore conducted to establish the effects of delayed harvest on moisture content, insect damage, moulds and aflatoxin contamination of maize in . Sixteen farmers were selected from Bayitambogwe sub-county, eight from each of the villages of Bugodi and Musita. Maize was sampled from each farmer’s field in 2003B and 2004A seasons at harvest stages of physiological maturity and after delayed harvest for 1, 2, 3 and 4 weeks. Each sample was analysed for mould incidence, moisture content, insect damage and aflatoxin contamination. In each season, mould incidence, insect damage and aflatoxin levels significantly (P < 0.05) increased with delayedtimeofharvest.Moisturecontentreducedwith delayed harvest time but the maize did not dry to the required safe storage moisture content of ≤15%. Seasonal effects were only significant for moisture content: the 2003B crop had consistently lower moisture content than 2004A crop. These results indicate that, for improved harvest quality of maize, farmers should harvest no later than 3 weeks after maize has attained physiological maturity.  2005 Society of Chemical Industry

Keywords: delayed harvest; physiological maturity; quality; maize

INTRODUCTION been reported to delay harvesting of their maize for Maize (Zea mays L.)isamajorstaplefoodfora a period varying from 1 to 4 weeks after physiological majority of the people in Uganda. In 2002, total maize maturity. However, field drying of maize by traditional production in Uganda was more than 750 000 metric methods falls short of attaining moisture levels that are tonnes produced on a total area of 560 000 hectares.1 safe for storage. It also leads to long-term exposure of The crop is usually physiologically mature 7–8 weeks the crop to infestation and damage by insects, birds, after flowering, at which time the grain contains rodents, wild animals and fungi.5 On average, field 35–40% moisture and has maximum dry weight. This losses due to these pests are 7–15%, but losses can is the time at which the crop should be harvested to be as high as 50% under extreme conditions.6 The avoid unnecessary losses in the field.2 However, in infestation and damage that starts in the field due Uganda, the time and method of harvesting maize to the above pests accounts for up to 80% of insect depend on weather conditions, the size of the crop infestation at the beginning of storage. This becomes and how quickly the farmer wants to utilize the crop.3 a great liability in storage. Most farmers prefer to leave the crop in the field to dry Aflatoxin contamination of maize in Uganda has before it is harvested. In this case, farmers harvest the been reported to start in the field and increase during dehusked cob from the standing plant. Other farmers storage. For example, in Mayuge district, aflatoxin cut the stem of the crop with the cob and let it levels as high as 10 and 700 ppb have been reported dry either on the ground or by piling them up in a in on-farm and market maize, respectively,7 and a standing position. Farmers in Mayuge district4 have number of traditional practices used by farmers have

∗ Correspondence to: Archileo N Kaaya, Department of Food Science and Technology, Makerere University, PO Box 7062, Kampala, Uganda E-mail: [email protected] Contract/grant sponsor: IPM CRSP (Received 18 October 2004; revised version received 15 March 2005; accepted 17 March 2005) Published online 19 August 2005  2005 Society of Chemical Industry. J Sci Food Agric 0022–5142/2005/$30.00 2595 AN Kaaya et al. been implicated. In this study therefore, the effect of prepared by mixing 68 g sodium chloride, 10 g malt delayed harvest on moisture content, insect damage, extract, 20 g agar and 1 L distilled water was used mould infection and aflatoxin contamination of maize for growing mould species requiring a high osmotic from Mayuge district was investigated. The findings of concentration.14 Ten kernels were placed directly on this study are very important in advising farmers how each agar plate. The plates were incubated upright at long they can leave maize in the field after attaining 30 ◦C for 42–72 h. After sufficient growth, some of the physiological maturity for best harvest and storage cultures that could not be identified were transferred quality. onto acidified PDA several times for purification and mould species were identified using the recommended manuals and keys.15,16 Earlier studies4,17 isolated and MATERIALS AND METHODS characterized the different species of moulds asso- Sampling ciated with harvested maize in Mayuge district and Sixteen maize farmers were selected from Mayuge reported that Aspergillus, Fusarium and Penicillium district, Bayitambogwe sub-county, eight from each of species were the most predominant moulds in the the villages of Bugodi and Musita. Mayuge district maize grains from the district. Therefore, this cur- is located in the eastern part of Uganda at an rent study did not characterize the different species of approximate altitude of 1070–1167 m above sea level, moulds in the different samples, but put more empha- with an average rainfall of 2200 mm per year and sis on Aspergillus, Fusarium and Penicillium spp. in the moderate temperatures of 21–27 ◦C throughout the kernels. year.8 Three maize samples (each sample composed of five cobs of almost same size obtained from five Aflatoxin analysis plants) were hand harvested from each farmer’s field in Each of the samples was divided into two replicate lots 2003B (July–August) and 2004A (January–February) and aflatoxins were extracted using methanol–water seasons at various times of physiological maturity and solution (80:20 vol) and quantified in parts per bil- delayed harvest for 1, 2, 3 and 4 weeks, following lion (ppb) using an Aflatest fluorometer following recommended methods.9 Thus, 48 samples were the manufacturer’s instructions (VICAM L.P., Water- collected at each harvest stage in each season. town, MA, USA). The detection limits were set at The samples were transferred on the same day to 0 ppb (lowest) and 22 ppb (highest). The range and the Department of Food Science and Technology, mean aflatoxin content (ppb) of the samples were Makerere University, and stored at −20 ◦Ctoprevent computed. postharvest accumulation of moulds and aflatoxins until analysis.10 Data analysis Data for moisture content, insect damage and aflatoxin Determination of moisture content levels in each season were summarized and subjected The samples collected at physiological maturity and to analysis of variance/least significant difference delayed harvest for 1, 2, 3 and 4 weeks were hand- (ANOVA/LSD) test18 to determine whether there shelled separately and divided into two replicate lots. were significant differences due to delayed harvest. The moisture content of each lot was determined by the standard air oven method.11 The samples were ◦ dried at 100 C to constant weight, and the mean RESULTS moisture content calculated on a wet basis. Moisture content Results of moisture content at different harvest stages Determination of insect damage are presented in Table 1. The moisture content of the Insect damage of the grains in each sample was maize grains in both seasons was significantly reduced assessed visually using a qualitative scale of 0–4, with delayed harvest time, but the maize did not dry to where 0 = no damage, 1 = low (from 1 to 10 seeds), the required safe storage moisture content of ≤15%.19 2 = medium (11 to 20 seeds), 3 = high (21 to 30 Seasonal effects were also found to be significant in seeds) and 4 = very high (>30 seeds).4 that the 2004A maize kernels had consistently lower moisture content than 2003B kernels. At physiological Isolation and identification of moulds maturity, the mean moisture content of the kernels was Fifty kernels of maize from each sample lot were 37% and was reduced to 24% in 2003B and 21% in assayed by direct plating technique for internal mould 2004A after 4 weeks’ delay in harvest infection.12,13 The kernels were surface sterilized for 1 min with 10% sodium hypochlorite (commercial Insect damage bleach, Jik), washed three times with sterile distilled Insect damage of maize grains significantly increased water and placed directly on malt extract agar (Becton with delayed time of harvest in the 2003B season Dickinson Microbiological Systems, Becton Dickin- but not in the 2004A season (Table 2). In the son and Company, Sparks, MD, USA) prepared by 2003B season, insect damage more than doubled mixing 33.6 g in 1 L distilled water, as recommended when harvesting was delayed by 2 weeks and increased by the manufacturer. In addition, malt salt agar media more than 10 times when the harvest was delayed

2596 J Sci Food Agric 85:2595–2599 (2005) Effect of delayed harvest on maize in Mayuge, Uganda

Table 1. Effect of delayed harvest on moisture content of maize from Table 3. Effect of delayed harvest on mould incidence of maize from Mayuge district of Uganda Mayuge district of Uganda

Moisture content (%)a Mouldy kernels (%)

Harvest stage 2003B 2004A LSD 2003B 2004A Harvest Mould Physiological maturity 37.39 37.12 NS stage species Range Mean Range Mean 1 week delay 32.65 28.81 0.57∗∗ 2 week delay 28.29 25.61 1.31∗ Physiological Aspergillus spp. 0–30 2.23 0–30 2.42 3 week delay 25.82 23.63 0.25∗∗ maturity Fusarium spp. 0–10 1.65 0–20 1.46 4 week delay 24.23 21.43 0.44∗∗ Penicillium spp. 0–10 0.24 0–10 0.08 LSD (P < 0.05) 0.877∗∗ 0.575∗∗ Others 0–30 2.36 0–20 0.95 1 week delay Aspergillus spp. 0–30 5.45 0–30 4.72 a Means are for 18 samples per harvest stage per season. Fusarium spp. 0–20 2.85 0–20 2.48 NS, non-significant (P > 0.05). Penicillium spp. 0–10 0.68 0–20 0.25 ∗ Significant (P < 0.05). ∗∗ Significant (P < 0.01). Others 0–40 3.50 0–30 2.59 2 week delay Aspergillus spp. 0–60 10.70 0–50 9.21 Table 2. Effect of delayed harvest on Insect damage of maize from Fusarium spp. 0–20 3.62 0–20 3.42 Mayuge district of Uganda Penicillium spp. 0–10 1.45 0–10 1.55 Others 0–40 8.56 0–30 7.86 a,b Insect damage 3 week delay Aspergillus spp. 0–60 14.48 0–80 12.42 Fusarium spp. 0–30 6.85 0–30 5.60 Harvest stage 2003B 2004A Penicillium spp. 0–20 3.84 0–10 3.12 Physiological maturity 0.11 0.11 Others 0–80 10.15 0–60 9.86 1 week delay 0.17 0.11 4 week delay Aspergillus spp. 10–100 48.25 0–100 38.56 2 week delay 0.35 0.22 Fusarium spp. 0–60 16.60 0–50 12.48 3 week delay 0.39 0.33 Penicillium spp. 0–20 4.12 0–20 3.96 4 week delay 1.5 0.39 Others 0–80 15.46 0–50 35.10 LSD (P < 0.05) 0.23∗ NS a Means are for 18 samples per harvest stage per season. Table 4. Effect of delayed harvest on aflatoxin levels of maize from b = = = Ranked from 0 to 4 (0 no damage, 1 low, 2 moderate, Mayuge district of Uganda 3 = high, 4 = very high). ∗ Significant (P < 0.05). Aflatoxin content (ppb)a NS, insect damage was not significant (P > 0.05). 2003B 2004A by 4 weeks. However, overall insect damage in both Harvest stage Range Mean Range Mean seasons remained low during the 4-week delayed harvest (Table 2). Physiological maturity 0–2.5 0.72 0–2.0 0.60 1 week delay 0–5.8 0.79 0–2.5 0.75 2 week delay 0–8.5 1.95 0–3.0 1.27 Mould infection 3 week delay 0–10 2.96 0–4.5 2.35 Results of mould infection indicate that Aspergillus, 4 week delay 0–12 5.53 0–8.5 4.87 Fusarium, Penicillium and other mould species were LSD (P < 0.05) 1.09∗ 0.92∗ isolated and identified in the maize kernels at each a Means are for 18 samples per harvest stage per season. harvest stage (Table 3). During both seasons, mould ∗ infection increased as maize harvest time was delayed. Significant (P < 0.01). The increase was more pronounced in Aspergillus spp. than in other mould species in both seasons. The times by week 3 of delayed harvest and more than occurrence of Aspergillus spp. in the kernels was also 7 times when maize harvest was delayed for 4 weeks. higher than that of other mould species. By week 4 The highest aflatoxin levels were found to be 12 ppb of delayed harvest, about 48 and 39% of the maize during season 2003B, and these were analysed in kernels in 2003B and 2004A seasons, respectively, had maize harvested after 4 weeks. In the 2004A season, been infected by Aspergillus spp., which was about 20 the highest aflatoxin levels were 8.5 ppb and were also times higher than in kernels harvested at physiological analysed in maize harvested after 4 weeks (Table 4). maturity (Table 3).

Aflatoxin levels DISCUSSION Levels of aflatoxin contamination of maize at different Field drying of maize in Uganda2 normally lasts harvest stages are presented in Table 4. Aflatoxin 4–7 weeks beyond physiological maturity. During this contamination of maize kernels started at physiological period, the moisture of the grain is reduced from the maturity and significantly increased with delayed time 35–40% level at physiological maturity to 16–20%, of harvest during 2003B and 2004A seasons. In both agreeing with the findings of our study. The moisture seasons, mean aflatoxin levels increased by about 4 content of the 2003B kernels was significantly higher

J Sci Food Agric 85:2595–2599 (2005) 2597 AN Kaaya et al. than that of the 2004A kernels, possibly due to the was increased, and the levels of aflatoxin were low at weather conditions. In Uganda, it always continues harvest (<20 ppb). Our findings showed a significant to rain during the harvest period in the B season, so increase but consistently low levels of aflatoxin. These that farmers who depend on open-sun drying have levels may increase during postharvest handling of problems drying their produce to safe storage levels.3 maize, thus exposing consumers to an aflatoxin health In Thailand, during the rainy season, standing maize hazard. having a moisture content of 27–30% at field maturity was found to have dried to 18–22% after 2 weeks 20 of field drying. The annual rainfall in Thailand is CONCLUSION −1 1280–2340 mm year , which is comparable to the The results of this study have indicated that delaying −1 8 1250–2200 mm year received in Mayuge district. harvest of maize for 4 weeks after physiological This may imply that reduction of moisture content maturity does not result in dry grains of safe storage of maize during field drying depends on weather, and moisture content but significantly increases insect may vary from place to place. Field drying helps to damage, mould infection and aflatoxin contamination reduce the moisture of the grain, thus reducing the and accumulation, thus negatively impacting on the 2 time required to dry the grains at home. Likewise, quality of harvested maize. It is uncommon for the moisture of the husks and of the overall cob is commercial farmers in Uganda to harvest maize at also drastically reduced. Thus, the crop will have less physiological maturity owing to over-reliance on open- weight to be transported to the farm yard and fewer sun drying; therefore, there is need to harvest earlier to problems drying the low-moisture crop. improve postharvest quality. Thus, it is recommended There was no significant increase in the number that farmers should harvest maize not later than of insect-damaged kernels in maize left to dry in the 3 weeks after the crop has attained physiological 20 field for 4 weeks in Thailand, disagreeing with the maturity. results of our study. However, insect infestation in maize has been reported to start in the field, and damage increases substantially during storage.21,22 The observed increase in insect damage in the 2003B ACKNOWLEDGEMENT season grain as compared to 2004A grain may be due This study was funded by IPM CRSP. We thank to differences in their moisture content as this has farmers from Mayuge for their contribution. been reported to affect insect infestation of the grain during storage. Although insect damage in our study remained low during the 4-week period of delayed REFERENCES harvest, infestation levels could have been higher and 1UBOS,Statistical Abstract: Uganda Bureau of Statistics, Entebbe (2002). thus increased the potential for grain damage during 2 Odogola WR and Henriksson R, Postharvest management storage. and storage of maize, in Technical Systems for Agriculture. Reports in the literature indicate that maize at UNDP/OPS Regional Programme on Agricultural Operations the time of harvest is typically infected with a Technology for Small Holders in East and Southern Africa, variety of fungi and, Aspergillus, Fusarium, Penicillium pp. 27–48 (1991). 23– 25 3 Kikafunda-Twine J, Kyetere DT, Bigirwa G, Kalule T and and Rhizopus species are among those reported, Wamaniala M, Maize, in Agriculture in Uganda Volume II: agreeing with our findings. The results of this study Crops, ed by Mukiibi JK. Fountain Publishers, Uganda, indicate that delayed harvest enhances the potential pp. 55–69 (2001). contamination of Aspergillus-produced aflatoxin in 4 Kaaya AN, Warren H and Adipala E, Molds and aflatoxin maize grown in Uganda prior to harvest, as has contamination of maize and groundnuts in Mayuge and Kumi . MUARIK Bull 3:33–41 (2000). 4 been reported. Other types of mycotoxins, like 5 Sauer DB, Contamination by mycotoxins: when it occurs fumonisins produced by Fusarium verticillioides24 and and how to prevent it, in Mycotoxin Fungi, Mycotoxins, zearalenones produced by F. graminearum,26 could Mycotoxicoses. An Encyclopedic Handbook. Vol. 3. Mycotoxicoses also be enhanced. of Man and Plants; Mycotoxin Control and Regulatory Practices, Aflatoxin contamination of corn in the field is ed by Wyllie TD and Morehouse LG. Marcel Dekker, New York, pp. 146–158 (1978). an important problem internationally, particularly 6 Boxall RA, A critical review of the methodology for assessing in the tropical and subtropical conditions that farm-level grain losses after harvest. Trop Dev Res Inst Bull favour infection and synthesis by Aspergillus flavus.27 C191 (1986). Aflatoxin contamination of maize in Uganda has 7 Kaaya AN, Warren H, Adipala E, Kyamanywa S, Agona JA and Bigirwa G, Effect of drying methods and storage time on been reported to start from the field and increases mould incidence, insect damage and aflatoxin levels in maize 7 during storage. In 2002, aflatoxin levels as high as grains, in Proceedings Integrated Pest Management Conference for 700 ppb were analysed in Ugandan maize obtained Sub-Saharan Africa, Kampala-Uganda, pp. 310–314. (2002). from traders.7 However, in our study aflatoxin levels 8 Rwabwoogo MO, Uganda Districts Information Handbook,5th in the kernels were consistently lower than the edn. Fountain Publishers, Kampala-Uganda, pp. 115–117 28,29 (2002). FDA/WHO regulatory levels of 20 ppb. Magan 9 Ware GM, Inspection, sampling and analysis of maize and and Lacey found no trend towards an increase in groundnuts for aflatoxin (1998). Available: www.fao.org/ aflatoxin contamination of maize as field drying time inpho/vlibrary/x0036e/X0036E04.htm [28 October 2002].

2598 J Sci Food Agric 85:2595–2599 (2005) Effect of delayed harvest on maize in Mayuge, Uganda

10 Anderson WF, Holbrook CC, Wilson DM and Matheron ME, drying) in controlling aflatoxin contamination (1998). Avail- Evaluation of peanut aflatoxin contamination in several able: www.fao.org/inpho/vlibrary/x0036e/X0036E04.htm [28 potentially resistant peanut genotypes. Peanut Sci 22:29–32 October 2002]. (1995). 21 Dunkel FV, The relationship of insects to the deterioration 11 AOAC, Official Methods of Analysis of AOAC International,6th of stored grain by fungi. Int J Food Micro 7:227–244 edn, 5th revision, Vol. 11. AOAC International, Gaithersburg, (1988). MD (1999). 22 Simpanya MF, Alotey J and Mpuchane S, Insect and mycoflora 12 Munimbazi C and Bullerman LB, Molds and mycotoxins in interactions in maize flour. Afr J Food Nutr Sci 1:3–8 (2001). foods from Burundi. J Food Prot 59:869–875 (1995). 23 Hesseltine CW and Bothast RJ, Mould development in ears of 13 Pitt JI and Hocking AD, Fungi and Food Spoilage, 2nd edn. corn from tussling to harvest. Mycol 69:328–340 (1977). Blackie Academic & Professional, London, pp. 21–437 24 Setamou´ MK, Cardwell F, Schulthess F and Hell K, Effect (1997). of insect damage to maize ears, with special reference to 14 Hanlin RT and Uiloa M, Atlas of Introductory Mycology. Hunter, Mussidia nigrivenella (Lepidoptera: Pyralidae), on Aspergillus Winston-Salem, NC, pp. 3–8 (1979). flavus (Deuteromycetes: Monoliales) infection and aflatoxin 15 Tuite J, Examining and identifying fungal cultures growing out production in maize before harvest in the republic of Benin. J from corn kernels, in A Laboratory Manual. Purdue University, Econ Entomol 91:433–438 (1998). West Layafette, IN (1982). 25 Cardwell KF, Kling JG, Maziya-Dixon B and Bosque-Perez NA, 16 Singh K, Frisvad JC, Thrane U and Mathur SB, An Illustrated Interactions between Fusarium verticollioides, Aspergillus flavus, Manual on Identification of Some Seed-borne Aspergillus, and insect infestation in four maize genotypes in lowland Fusarium, Penicillium and their Mycotoxins, 1st edn. Danish Africa. Phytopathology 90:276–284 (2000). Government Institute of Seed Pathology for Developing 26 Siame BA and Lovelace CEA, Natural occurrence of Zear- Countries, Hellerup (1991). alenone and Trichothecene toxins in maize-based animal 17 Sseruwu G, Fungal microflora causing maize ear rots in feeds in Zambia. J Sci Food Agric 49:25–36 (1989). Uganda. MSc thesis, Department of Crop Science, Makerere 27 Bucio-Villalobos CM, Guzman-de-Pe` na˜ D and Pena-Cabriales˜ University, Kampala (2003). JJ, Aflatoxin synthesis in corn fields in Guanajuato, Mexico. 18 Genstat 5, Release 3.2, PC/Windows NT. Lawes Agricultural Rev Iberoamericana de Mycolo 18:83–87 (2001). Trust, Rothamsted Experimental Station (1995). 28 Grybauskas AP, Thomison PR and Cassel EK, Aflatoxins. 19 Magan N and Lacey J, Ecological determinants of mould growth Maryland Coop. Ext. Fact Sheet 444. P88/R2000 (2000). in stored grain. Int J Food Micro 7:245–256 (1988). 29 Mphande FA, Siame BA and Taylor JE, Fungi, Aflatoxins 20 Nagler M, Buangsuwon D, Jewers K, Faungfupong S, Wong- and cyclopiazonic acid associated with peanut retailing in urai A, Nagler C and Tanboonek P, The role of leaving Botswana. J Food Prot 67:96–102 (2004). maize unharvested in the field after field maturity (field

J Sci Food Agric 85:2595–2599 (2005) 2599