Natural Resistance ofbuckwbeat Seeds and Products to Storage Pests

Transcription

1 Proceedings ofthe C)'h international Symposium on Buckwheat. Prague 2004 Natural Resistance ofbuckwbeat Seeds and Products to Storage Pests Dolores Ciepielewskat, Lncja Fornae University ofwarmia and Mazury in Olsztyn 1 Chair ofenthomology 2Chair ofplant Chemistry andprocessing ABSTRACT The natural resistance of buckwheat and buckwheat products against storage pests is not well known. The results of storage pests development on whole and dehulled buckwheat seeds have demonstrated that many pests lived longer than three weeks and some of them were able to reproduce. Special attention was paid to developmental cycle of Trogoderma granarium. which depends ofvariety. Keywords: buckwheat, variety, resistance, storage pests. INTRODUCTION Owing to their chemical composition, buckwheat seeds are a uniquely valuable raw material for production of foodstuffs. It is so because of the high biological value of buckwheat proteins and their characteristics, the low energy value of starch and the content of macro- and microelements. It needs to be emphasised that buckwheat proteins do not contain a sequence of amino acids rich in glutaminic acid and proline, which means that they are free from toxic a gliadins, and are therefore safe in diets for children who suffer from coeliac disease or for adults who show symptoms of parenteral coeliac disease. The fact that they can be used for production of food which fulfils the requirements set in therapeutic or prophylactic diets means that more attention must be paid to the hygienic quality ofbuckwheat seeds, including a potential threat ofcontamination by storage pests and their toxic metabolites. In general, it is believed that whole seeds of buckwheat are equipped with a complex and effective mechanism of resistance to infestation by storage pests. But is this so? What are the recognised elements ofthe natural resistance of buckwheat seeds to the growth and development of storage pests? Seed coat The morphology of a buckwheat nutlet is typical of this species. Of particular importance is the thickness of the seed cover (about 80 ~) and the strength of its interaction with the aleurone layer (fig. Ia, 1b, 1c). Another interesting element in the morphology of the two layers ofthe seed cover is their fibrous structure with a spiral arrangement of cells. Apart from the physical characteristics of the cover, the mechanism of natural resistance is strongly influenced by the chemical composition ofseeds. Hulls ofbuckwheat seeds contain ca 80% of fibre, including 60% of acid detergent fibre and 18% ofhemicellulases and 30% of cellulases (AMAROWICZ, FORNAL 1987). Due to such high percentages of cellulases and lignins, buckwheat hulls are not used for food production. For the same reason, they are not favoured by insect pests. In addition to the high content offibre, buckwheat hulls have been determined to contain 4% of protein and to be rich in macroe1ements and rutin (DIETRYCH-SZOSTAK, PLOSZYNSKI, 1988). ZADERNOWSKI et al. (1992) proved that buckwheat hulls contain many phenolic compounds, including tanins, which are condensed po1yphenols (tab. 1). Tanins deserve special attention, mainly because of their antibacterial, antineoplastic and antioxidative properties as well as their ability to inhibit the activity of a. amylase and depress the enzymatic availability ofproteins (LUTHER 1992). Another important group ofphenolic compounds consists of flavonoids, of which rutin and isovitexin appear in largest amounts (DIETRYCH-SZOSTAK, OLESZEK 1998). 639

2 at, Prague 2004 Fig. 1 Microstructure ofbuckwbeat seed (cross section). a) and b) cross section of seed, c) microstructure ofseed coat. (FORNAL ETAL. 1981). Tab. 1 Total amount of phenolic compounds, tannins and derivatives ofphenolic acids (ZADERNOWSKI et al. 1992) Total Tannins Derivatives Materials poliphenols ~ [rog/l GOg] ofphenolic acids...[mglloogj_ Buckwheat groats Buckwheat hull Lentil seeds Cotyledons The chemical and biochemical composltlod of proteins seem noteworthy in the chemical composition of the buckwheat endosperm (EGGUM 1980, SKERRIT 1986). However, the enzymatic availability of proteins is inhibited by the presence of inhibitors of highly thermostabile proteases (IKEDA et al. 1990, 1991). Also a-amylase protein inhibitors imply strong inhibition ofawamylase ofthe pancreas and saliva (IKEDA 1984). Buckwheat starch differs from cereal starch in many physical and physicochemical characteristics as well as in the amylolitic availability (SORAL-S,MlETANA et al. 1984, ACQUISTUCCI and FORNAL 1997, QlAN et al. 1998). This brief review of the most important chemical components of buckwheat seeds indicates the complex nature of their hypothetical natural resistance to infestation by storage pests. The natural resistance of buckwheat seeds is made up by some elements present in the seed cover as well as the cotyledons. Should the structure of the seed coat, and especially the high content of tanins, act as an important barrier to the development of insect pests, buckwheat products from dehulled seeds can be at a greater risk ofbeing infested. Development of some storage pests on whole and dehulled buckwheat seeds Results of several entbomogical studies have demonstrated than many pests, except Acanthoscelides obtectus, lived for over three weeks on whole or dehulled seeds (tab. 2) (PTERZYNOWSKA-KoRNIAK et al., 1991, ZADERNOWSKl et at., 1992, CIEPIELEWSKA et al., 2000). 640

3 Proceedings o/the 9th International Symposium on Buckwheat, Prague 2004 Tab, 2 Death rate ofinsects rrowing on whole and dehulled seeds ofbuckwheat. (ZADERNOWSKl et al. 1992) 100% death rate ofinsects (weeks) Kinds ofinsects Dehulled seeds Whole seeds Sitophilus oryzae Rhizopertha dominica Oryzaephilus surynamensis Acenthoscelides obtectus Cryptolestes ferrugineus Sitophilus granarius Tribolium confusum Tribolium destructor Anagasta kuehniella c - continuing to live r - reproducing 4 30 c, r 5 3 loc 15 c 4 30 c, r C 15 c 11c lie Four of the species tested (Tribolium confusum, T. destructor, Angasta kuehniella and Rhizopertha dominica) survived for over 11 weeks and reproduced on dehulled seeds, while two of them (R. dominica and A. kuehniella) did so on whole buckwheat seeds too, Some species were unable to reproduce, although they foraged on both whole and dehulled seeds for 10 (Cryptolestes ferrugeneus) and 15 weeks (Sithophilus granarium). Insects reproduced better on dehulled buckwheat seeds. Tribolium confusum and T. destructor were the most sensitive to the presence of hulls. The rate of infestation and the behaviour of insects is most probably closely connected with the characteristics of hulls, and especially the content of tanins. Some earlier research conducted by GOL~BIOWSK.A et al. (1976) suggests that as a habitat buckwheat groats (dehulled and roasted buckwheat seeds) are as acceptable to the grain weevil as grains of rye, wheat or maize (tab. 3,4). Barley groats are the most preferred habitat. A comparison of these two types of groats, barley and buckwheat, suggests that buckwheat groats can contain some components which limit the amount of food ingested by pests and hinder the number of offspring per one beetle and the control number of offspring (tab. 3). No such significant differences between the two types of groats have been found for the grain weevil (tab. 4). Tab. 3 Choice of food by grain weevil beetles (GOL~BIOWSKA et al. 1976). Products/grain Maize Wheat Rye Rice Buckwheat groat Barley groat Feeding mixture Amount offeed perone Number ofbreed per one irnago/cockchafer imago/cockchafer Control number of breed

4 Proceedings ofthe 9th International Symposium on Buchvheat. Prague 2004 Tab. 4 Choice offood by grain weevil ofspring beetles (GOL~BIOWSKA et al. 1976). Products/grain Amount offeed per one cockchafer in 10 days [mg] Number ofbreed per one female Weight of progeny cockchafer [mg] Maize Wheat Rye Rice Buckwheat groat Barley groat l Development and foraging by the grain weevil (Trogoderma granarium) The grain weevil (Trogoderma granarium) belongs to an omnivorous species, which is responsible for large losses of stored foodstuffs. It is tolerant to insecticides and can starve for a long time (BANKS 1977). On average, one larva of the grain weevil eats 18 mg of grains daily and leaves 14.4 mg of dust, which contains exuviae and hooked setae. Cast larval skins and hairs can cause allergies and inflammations of mucous membranes and conjunctivas in the technical staff working in storing facilities (GoLEBIOWSKA 1976, ALDRYHIN & ADAM 1992). Trogoderma granarium is the only storage pest which appears on the list ofquarantine species prepared by the European Plant Protection Organization. Several relationships have been noticed in the course of studies on the development of the grain weevil on buckwheat seeds and products conducted in Poland (CIEPIELEWSKA et al. 2000, NIEGOWSKA 2001). These investigations involved three buckwheat cultivars, whole and dehulled coarsely and finely ground seeds (tab. 5). Tab. 5 The size ofbuckwheat groat and flour Variety Buckwheat~ Size Groat ~ F_Io_u... r~ Hruszowska Emka Kora > 3.6 > 3.6 > <F<2.5 < <F<2.5 < <F<2.5 < 80 The duration of the development cycle of the grain weevil was different on whole buckwheat seeds and on buckwheat groats. The differences occurred in the length of the embryonic and larval stages and in the total development period (tab. 6). The two developmental stages took the longest time on seeds of the cultivar Kora. The development of the grain weevil on buckwheat groats showed a reverse tendency. The duration of a developmental cycle stage on buckwheat, whichever cultivar or granulation fraction, was longer than on the control grain, the grain ofcv. Almari wheat. 642

5 Proceedings ojthe 9'~ International Symposium on Buckwheat, Prague 2004 Tab. 6 Duration ofthe developmental cycle ofthe grain weevil (Trogoderma granarium). (NIEGOWSKA 2001). Variety Size Period ofdevelopment ~ Embryonic Larval Pupal Total Hruszowska Emka whole Kora Hruszowska <F<2.5 Emka rom Kora Hruszowska Emka F<!!m Kora Control whole Fig.2 Mean mortality ofthe grain weevil (Trogoderma granarium). (NIEGOWSKA 2001) ~e ~ 30 ~ 25 " ō 20.0 i3 15-1::: o 10 ~ 5 o whole 2,2<F<2,5mm F< 80jJm l I. Control. Hruszowska o Emka.~-.K~rall The highest mortality rate oflarvae was observed on whole seeds ofthe cultivars Kora and Emka (fig. 2). No dead larvae were found in groats from the buckwheat cultivars tested. Observations on buckwheat flour yielded different results. In the flour produced from seeds of the cultivars Hruszowska and Kora, the mortality rate of larvae was much lower than on whole seeds. The flour from seeds of cv. Emka was exceptional in that the mortality rate of larvae recorded there was several per cent higher than on whole seeds or in the flour from the cultivars Hruszowska and Kora. Higher mortality of larvae in flour (F < 80llm) may have been caused by worse feeding as well as less fabourable biological conditions. Gas exchange in fine flour is impeded, the concentration of metabolites produced by pests increases and the amount of oxygen decreases. The total developmental cycle in flour lasted from 37 to 42 days, depending on a buckwheat cultivar. As such, it was longer than in groats (fig. 3, tab. 6). 643

6 Proceedings ofthe 9'h International Symposium on Buckwheat. Prague 2004 Fig.3 Development cycle of the grain weevil (Trogoderma granarium) on buckwheat nuties ground to F< 80!!m. (NIEGOWSKA 2001) i C/J :s.., 25 ' ~ o control embryonic larval I i I pupal I The results of the statistical analysis, Freeman-Tykey's transformation and Duncan's test, confirmed high natural resistance of buckwheat seeds to the foraging by T. granarium. The cultivars tested were classified into two uniform groups: resistant (A) and less resistant (B). Seeds of cv. Emka were classified as showing resistance similar to that of grains of the cv. Alman wheat. Buckwheat groats and flour from any of the cultivars examined were classified into a group ofproducts in which the developmental cycle ofthe pest was similar to that observed on the wheat grains analysed_ The analysis of variance of the feeding preferences shown by the grain weevil showed a highly significant effect of a cultivar and granulation (tab. 7). Tab. 7 F emp test values from the analysis of variance for the larval stage of the grain weevil (Trogoderma granarium) growing on whole buckwheat nutlets and ground buckwheat products (NIEGOWSKA 2001). Source ofvariability Degrees offreedom Mean square Empirical F SD Variety ** Granulation ** Variety x Granulation ** Error ** - high statistical significant SUMMARY Storage pests can infest and develop on whole buckwheat seeds as well as on buckwheat products. Pests tend to prefer dehulled buckwheat seeds (groats) for foraging and as a habitat for reproduction. This tendency was confirmed for Rhizopertha dominica, Tribolium confusum, T. destructor and Angasta kuehniella. Another important finding is the 644

7 Proceedings a/the 9th International Symposium on Buckwheat, Prague 2004 capability of Trogoderma granarium to settle and develop on buckwheat whole seeds, groats or flour. REFERENCES ACQUSTUCCI R., FORNAL J. (1997): Italian buckwheat (Fagopyrum esculentum) starch: physicochemical and functional characterization and in vitro digestibility. Nahrung 41 (5): ALDRYHIM Y.N., ADAM B.E. (1992): The biology of Trogoderma granarium (Everts) (Coleoptera: Derrnestidae) in Central Province of Saudia Arabia. J Kind Saud Univ. Agric. Sci. 4(1): 79, 85. AMAROWICZ R., FORNAL L. (1987): Characteristic of buckwheat grain mineral components and dietary fiber. Fagopyrum 7: 3-6. BANKS H,J. (1977): Distribution and establishment of trogoderrna granarium Everts (Coleoptera: Dennestidae): climatic and other influences. J StoredProd. Res. 13: CIEPIELEWSKA D., FORNAL L., POPLAWSKA M. (2000): Infestation of buckwheat and its products by pests in storage facilities. 1. Plant Protection 40(1): DIETRYCH-SZOSTAK D., PLOSZTNSKJ M. (1988): The value of hulls and postharvest residue of buckwheat in feeding. Fagopyrum 8: DrETRYCH-SZOSTAK D., OLESZEK W. (1998): The composition and concentration of flavonoids in buckwheat groats and hulls. Pol. J Food Nutr. Sci. 7/48, No 2 (S): EGGUM B.O. (1980): The protein quality of buckwheat in comparison with other protein sources of plant or animal origin. Proceedings ofthe Buckwheat Symposium. Ljublana, FORNAL L., CIEPIELEWSKA D. (1994): Naturalnaodpomosc nasion gryki na porazenie przez szkodniki magazynowe. Materialy IX Krajowego Sympozjum "Gryka roslina altematywna". Siedlce, FORNAL 1., SORAL-SMIETANA M., FORNAL L (1981): Buckwheat groat production. Part II. The changes in the ultrastructure of buckwheat (Fagopyrum esculentum Moech) during processing. Die Nahrung 25(4): GOL~BIOWSKA Z. (1981): Sk6rek zbozowy (laszcz koprowiec) Trogoderma granarium Everts (Co1eoptera:Dermestidae)- kwarantannowy szkodnik produkt6w przechowalniczych. Prace lor 2: GOL~BIOWSKA Z., NAWROT 1., PRJ\DlYNSKA A. (1976): Studia nad szkodliwosci't kilku gatunk6w chrz'tszczy zeruj'tcych w ziarnie zb6z. Prace Naukowe lor 18(2): IKEDA K., SHIDA K., KrSHIDA M. (1984): a-amylase inhibitor in buckwheat seed. Fagopyrum 14,3-6. IKEDA K., SAKAGUCHI T., NISffiMURA A. (1990): Changes in the functional properties of buckwheat protein on heating. Fagopyrum 11: IKEDA K., SAKAGUCffi T., KUSANO T., YASUMOTO K. (1991): Endogenous factors effecting protein digestibility in buckwheat. Cereal Chem. 68(4): LUTHAR Z. (1992): Phenol classification and tanin content ofbuckwheat seeds. Fagopyrum 12, NIEGOWSKA M. (2001): Rozw6j sk6rka zbozowego (Trogoderma granarium Everts) w wybranych nasionach i ich przetworach., Ph.D. thesis UWM Olsztyn, PIERZYNOWSKA-KORNIAK G., CIEPIELEWSKA D., FORNAL L. (1991): Taniny gryki jako naturalny czynnik hamuj~cy rozw6j szkodnik6w magazynowych. Materialy XXXI Sesji Naukowej lor. Cz.II,: QIAN JUNE., RAYAS-DUARTE P., GRANT L. (1998): Partial characterization ofbuckwheat (Fagopyrum esculentum) starch. Cereal Chem.75(3): SKERRITT J.R. (1986): Molecular comparison of alcohol soluble wheat and buckwheat proteins. Cereal Chem.63(4): Soral-SMIETANA M., FORNAL L., FORNAL J. (1984): Characteristics ofbuckwheat grain starch and the effect of hydrothermal processing upon its chemical composition, properties and structure. Starch/Starke 36(5): ZADERNOWSKI R., PIERZYNOWSKA-KORNIAK G., CIEPIELEWSKA D., FORNAL L. (1992): Chemical characteristic and biological functions of phenolic acids of buckwheat and lentil seeds. Fagopyrum 12: