The Effect Of High Temperature And Modified Atmospheres On Insect Pests In Wheat Flour

The effect of high temperature and modified atmosphere on Tribolium castaneum(Herbst) and Lasioderma serricorne (F.)(Coleoptera: Anobiidae), two important pestinsects in wheat flour at60-80%R.H. was investigated, and the important qualityindices for wheat flour were also evaluated after heat-treatment and modifiedatmosphere packaging treatment. The main results were the following:(1) High temperature is an important factor resulting in insect death. Theinstantaneous high temperature treatment had a strong inhibition for differentdeveloping stages of T. castaneum and L. serricorne. For the treatments without wheatflour, mortality of each developing stage increased with increasing temperature andexposure time. Adults were the most heat-tolerant stage at50℃without flour.However, when exposure temperature equal to or under45℃, or equal to55℃orabove, no significant differences were observed in any exposure time. The mortalityof larvae, adults and pupae were0%through the set exposure times at45℃. Themortality of larvae, adults and pupae were73.33%,0%,23.33%after120s at50℃respectively. When the treatment temperature increased to55℃，the mortality of allstages were100%on the set exposure times. For the treatments with50g of wheatflour, the exposure times had significant effect on the mortality of adults, and nosignificant effect on the mortality of pupae and larvae of T. castaneum at55℃and60℃. When the treatment temperatures were55℃or above, the mortality of T.castaneum adults reached100%after90s exposure time or above. When thetreatment temperatures were60℃or above, the mortality of T. castaneum larvaereached100%after90s exposure time or above. When the treatment temperatureswere65℃or above, the mortality of T. castaneum pupae reached100%after75sexposure time or above.At the set treatment temperatures, the pupae of L. serricorne were the mostheat-tolerant stages, following the eggs, adults and larvae. When the treatmenttemperatures were60℃or above, the mortality of the L. serricorne larvae reached100%after75s exposure time or above. When the treatment temperatures were60℃or above, the mortality of the L. serricorne adults and eggs reached100%after90s exposure time or above. When the treatment temperatures were60℃or above, themortality of the L. serricorne pupae reached100%after120s exposure time or above.(2) The effect of different exposure times on the important quality indices ofwheat flour were evaluated after heat-treatment at60,65and70℃. The main resultsof moisture content, free fatty acid value and the whiteness were the following:Generally, moisture contents declined with an increasing temperature and exposuretimes and the free fatty acid values increased slightly with an increasing temperatureand exposure time. For the wheat flour with initial moisture contents of12.80%, themoisture contents were10.64%,10.93%and10.33%at60,65and70℃after120s,respectively, and the free fatty acid value were25.57KOH mg/g (w.b.),24.37KOHmg/g (w.b.) and25.60KOHmg/g (w.b.), respectively. However, the treatmenttemperatures had no effect on the whiteness.(3) Modified atmosphere packaging (MAP) had a strong inhibition effect oninsects in wheat flour. When wheat flour is stored in hermetically sealed bag, itproduced100%T. castaneum adults mortality at25℃after6d and the mortality ofL.serricorne adults was55.00%after8d. However, eggs, larvae and pupae survived.When samples treated with O2absorbers, it produced100%mortality of larvae, pupaeand adults of T. castaneum after4d and produced90%mortality of eggs, larvae,pupae and adults of L.serricorne after6d. When the high nitrogen (N2) concentrations(97%) were applied, the mortality of larvae, pupae and adults of T. castaneum was100%after4d and the mortality of eggs, larvae, pupae and adults of L.serricorne wasalso100%after6d. Different insect species and developmental stages had differentsensitivity to the MAP treatment.(4) MAP had a certain impact on the quality of wheat flour. Under certainconditions, MAP had prevented dissipating of the moisture content of wheat four, butthe prevention ability gradually declined with an increasing treatment time; comparedwith conventional packaging, MAP had little impact on the fatty acid content. Whensamples treated with O2absorbers, it speeds up the whiteness of wheat flour. Otherstorage methods had no significant effect the whiteness of wheat flour.