Presence of Starch/Protein Aggregates in the Endosperm of Corn

Abstract

It is common knowledge that the presence of so called .'grits" and other structures in process streams of the corn wet milling process leads to starch yield losses by incomplete starch/gluten separation. The nature of these problematic structures was investigated by isolating them from the process streams and analysing their morphology by means of epifluorescence microscopy using specific dyes. Additional evidence was obtained by specific enzymatic degradation and subsequent microscopic observation. Using the same technique on thin cross sections from whole corn kernels, the location and source of these structures could be identified. Grits are dense particles from the horny endosperm, consisting of a three dimensional honeycomblike protein matrix filled with small starch granules. Many grits show the regular cell shape found in endosperm cells and are still enclosed by the fibrous cell wall. In other process streams, aggregates of protein lumps with trapped large and small starch granules occur frequently. A small fraction of fibrous material was also found to be enclosed in the protein matrix. These "sticky" aggregates often occur along with a large percentage of extremely small starch granules or fragments. Occasionally, very small "grits"-like particles were present. Based on these findings, explanations can be found for the loss of starch and for the difficulties in the starch-gluten separation stage in the industrial corn wet milling process Vorkommen von Starke/Protein-Aggregaten im Endosperm von Mais. Es ist allgemein bekannt, daR die Anwesenheit sogenannter .,Grits" und anderer Strukturen in ProzeBstromen des Mais-NaBmahlprozesses zu Ausbeuteverlusten an Starke fuhren und die Trennung in Protein und Starke erschweren. Die problematischen Strukturen wurden aus ProzeBstromen isoliert und ihre Beschaffenheit durch Analyse ihrer Morphologie mit Hilfe der Epifluoreszenz-Mikroskopie unter Verwendung spezifisch anfarbender Farbstoffe untersucht. Zusatzliche Beweise wurden durch spezifischen enzymatischen Abbau und nachfolgender mikroskopischer Beobachtung erhalten. Mit der gleichen Technik an Diinnschnitten von ganzen Maiskornern wurde der Ursprung dieser Strukturen lokalisiert. Grits sind dichte Partikel vom hornigen Endosperm, die aus einer dreidimensionalen bienenwabenahnlichen Proteinmatrix bestehen, welche mit kleinen Starkekornern besetzt ist. Viele Grits haben die gleich-maBige Zellform wie Endospem-Zellen und sind noch von faseriger Zellwand umhullt. In anderen ProzeRstromen treten haufig Aggregate von Protein-Klumpen mit eingeschlossenen groRen und kleinen Starkekornern auf. Ein geringer Anteil von eingeschlossenem faserigem Material wurde ebenfalls nachgewiesen. Diese ,,klebenden" Aggregate treten haufig gemeinsam mit einem hohen Prozentsatz extrem kleiner Starkekorner oder ihrer Fragmente auf. Gelegentlich waren sehr kleine ,.grits"artige Teilchen anwesend. Aufgrund dieser Befunde konnen Erklarungen fur die Starkeverluste und die Schwierigkeiten bei der Starke-Protein Trennstufe im industriellen Mais...

Starch Biosynthesis. II. The Statistical Model for Amylopectin and Its Precursor Plant Glycogen

“…Another possibility would be that a few of the amylose chains are transferred to the newly formed amylopectin to perhaps form triple helices. That is, these long chains do not exist in waxy starches [38][39][40] but are observed in amylose containing starches. In addition, the existance of the long chain in these amylopectins may be due, not to the transfer of a long branch which could be subsequently branched further, but rather may be due to the transfer of relatively short chains from the GBSS to the precipitating amylopectin, which subsequently complex with the amylopectin aggregates to possibly from triple helicies with existing double helicies in interacting amylopectin molecules.…”

“…Different protein-amylopectin aggregates, such as granular bound starch synthase enzymes in dent but not in waxy corn, could explain the differences in disaggregation properties of waxy, immature sweet corn and dent corn amylopectins. Such complexes are known to exist [39][40][41] and most likely are involved in the staling of bread [45]. Another possibility would be that a few of the amylose chains are transferred to the newly formed amylopectin to perhaps form triple helices.…”

“…The fact that 90 % DMSO, which is an excellent agent for destroying hydrogen and hydrophobic bonds as pointed out previously [38], was unable to break apart these aggregates of waxy corn amylopectin, whereas in our studies [2,34,35] sodium phosphate was able to do so with respect to the same type (waxy) of corn amylopectin, suggests that waxy amylopectin aggregates may be due to ionic bonds (salt bonds) involving either A) phosphate groups on the waxy amylopectin and positively charged groups on associated proteins, B) phosphate -M ++ -phosphate bonding (where M ++ might be Mg ++ ) between amylopectin phosphates or between amylopectin and proteins, or C) covalently linked proteins to amylopectin which in turn produce ionic bonds between other such linked proteins or with other amylopectin molecules. Protein-amylopectin aggregates have been known to exist for some time and recently have been studied with respect to various proteins [39,40]. Previous studies showed a maximum in interactions of wheat proteins and dextrans [41].…”