B2-Phase Transitions B2-O1 HIGH-RESOLUTION AND TIME-RESOLVED XRD STUDIES OF COCOA BUTTER LEAD TO BETTER CHOCOLATE

Henk Schenk, René Peschar
unpublished
Am ster dam, The Neth er lands. (h.schenk@uva.nl) Crys tal li za tion of co coa but ter is the crit i cal step in mak ing choc o late and con fec tion er ies. Poorly crys tal lized choc olate may re sult in the for ma tion of fat bloom, a greyish-white film at the choc o late sur face. Co coa but ter has been sub ject to re search for many years re sult ing in at least six dif fer ent poly morphs, in di cated by Greek let ters g, a, b' and b. In good qual ity choc o late pre dom i nantly the
more » ... dom i nantly the b(V)polymorph is pres ent, but may be also the b(VI)-phase. X-ray pow der dif frac tion (XRD) is a very use ful technique to iden tify the fin ger print re gion (d = 3.0 -6.0 C) of the co coa but ter poly morphs, which are dif fer ent for all. In fat re search XRD has the ad van tage over DSC of giv ing un am big u ous phase in for ma tion. Time-re solved XRD (trXRD) is a very suit able tool for study ing the phase transfor ma tions of the sys tem as well as for fol low ing melt ing and so lid i fi ca tion pro cesses. It is be ing used ex ten sively in our re search and may be pre sented in mov ies. Also full XRD pat terns, in clud ing peaks at long d-spacing val ues, are be ing used to char ac ter ize the var i ous cocoa-but ter phases. Fur ther more, the com po nents of co coa but ter, the triacylglyceroles (TAG, see fig ure) , are sub ject to struc ture de ter mi na tion stud ies us ing High-Res o lu tion Syn chro tron data. This even tu ally will lead to more suitable mo lec u lar mod els for co coa but ter to un der stand its crystallisation and phase trans for ma tion. Both sin gle crystal and pow der meth ods are be ing used, but, re mark ably, the lat ter meth ods are more suc cess ful as it is very dif fi cult to ob tain suit able sin gle crys tals and to han dle them. In order to un ravel the mech a nism of fat bloom, we re cently took up the crys tal struc ture so lu tion of the b(V)polymorph of cocoabutter and we expect to be able to report on this research at the meeting. Crys tal li za tion of co coa but ter in the b phase di rectly from the melt un der static con di tions is only pos si ble employ ing the mem ory ef fect of co coa but ter [1]. When b-phase co coa but ter is heated be low a max i mum tem per ature and above the melt ing end point, it re-crys tal lizes in the b-phase at crys tal li za tion tem per a tures. The in flu ence of the max i mum and crys tal li za tion tem per a tures on the re-crys tal li za tion be hav iour has been in ves ti gated for cocoa but ter from Bahia (Brazil). Re-crys tal li za tion into the b(VI)-phase ap pears to be faster than into the b(V)-phase. Struc tural in for ma tion on the seed ma te rial ini ti at ing the re-crys tal li za tion pro cess has been col lected through Small-An gle X-ray Scat ter ing. High-melt ing SOS-rich seeds in tri ple chain-length pack ing ini ti ate the rapid-starting re-crys tal li za tion. The seed crys tals ini ti at ing the [3] Schenk, H., Visser, P. And Peschar, R. , ab stract ISF 25, Bor deaux, 2003. Ó Krystalografická spoleènost
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