Stability of α‐L‐aspartyl‐L‐phenylalanine methyl ester hydrochloride in aqueous solutions

Abstract

The stability of USAL (I-L-aspartyl-L-phenylalanine methyl ester hydrochloride) was studied in solutions in relation to the pH value ( I . 10-6.95 at 20 "C), the temperature (20-80 "C at pH 2.2) and the ionic strength (0.16---2.0 at 20 'C and pH 4.0). The effects of pH and temperature of the medium were very significant.From the point of view of the stability the optimum pH value lies in the pH range 2.5-4.5 and at lower temperature. The ionic strengthdid not affect the stability in the tested range. Theeffectsofcitric acid (0-10 7;) and sucrose (0-75 "G) were also investigated. An addition of citric acid exhibited an effect on USAL stability corresponding to the shift of pH value that it caused. The Occurrence of sucrose in the solution had a favorable effect at higher concentrations.Artificial sweeteners based on peptides belong to the recently discovered sweet-tasting substances [l]. It seems that from the whole series of peptides known so far [2], the dipeptidic sweeteners a-L-aspartyl-L-phenylalanine methyl ester (ASPARTAM) and a-L-aspartyl-L-phenylalanine methyl ester hydrochloride (USAL) belong to the most promising for application as sweeteners. They are suitable both for low-energy foods and for diabetics diet. Some properties of ASPARTAM and the possibilities of its application have been already described in the literature [2--51. The stability ofthis sweetener is preimposed by its dipeptidic character. The temperature and the pH of the medium represent the main factors affecting the stability in aqueous solutions. However, in food systems an additional series of factors may exhibit their effects, i. e. the other food components and in some cases the microbiological influence might be expected [6].The stability experiments were performed in model systems, in citrate-phosphate buffers and in the solutions of citric acid and sucrose. The citrate-phosphate buffers very closely approximate by their pH values to the media characteristic for foods. The solutions of citric acid and sucrose form models of fruit sirups that have been used in the production of soft drinks. Experimental

Aspartame Degradation Kinetics as Affected by pH in Intermediate and Low Moisture Food Systems

“…1 and from the data in Table 1, it was evident that for the three pH levels, aspartame degradation in reducedmoisture systems occurred fastest at pH 7, was slower at pH 3, and had the lowest rate at pH 5. As mentioned previously, similar results were observed in solutions by Prude1 and Davidkova (1981) and Stamp (1990). Homler (1984) also reported similar results at 40 and 55°C.…”

Aspartame Degradation in Solution As Impacted by Buffer Type and Concentration

“…The flow rate was set at 1.0 mL/min, and UV absorbance was read at 214 nm. Rate constants with 95% confidence limits were calculated using pseudo-first-order kinetics as done previously (Prudel and Davidkova, 1981; Tsoubeli and Labuza, 1991;Bell and Labuza, 1991a,b).…”

“…The impact of pH on aspartame degradation has been thoroughly examined in liquid and solid systems. Aspartame is most stable between pH 4 and 5 with increased acid hydrolysis at lower pH values and increased base catalysis at higher pH values (Prudel and Davidkova, 1981;Homier, 1984; Prudel et al, 1986;Ozol, 1986;Bell and Labuza, 1991a,b;Tsoubeli and Labuza, 1991; Skwierczynski and Conners, 1993). The effect of temperature on aspartame degradation has also been evaluated (Homier, 1984; Prudel et al, 1986;Ozol, 1986;Araman and Temiz, 1988;Bell and Labuza, 1991a;Tsoubeli and Labuza, 1991).…”

“…However, many researchers have not evaluated the effect of buffer concentration and type on aspartame degradation during the course of their studies. For example, the study by Prudel and Davidkova (1981) used phosphate-citrate buffer blends at various pH values; therefore, individual buffer effects could not be distinguished. In addition, the buffer concentrations were not held constant, inhibiting the ability to differentiate between pH effects and concentration effects.…”

Peptide Stability in Solids and Solutions

“…The impact of pH on aspartame degradation has been examined in liquid and solid systems. In solutions, aspartame is most stable between pH 3.5 and 5, with increased acid hydrolysis at lower pH values and increased base catalysis at higher pH values (Prudel and Davidkova, 1981; Prudel et al, 1986; Ozol, 1986; Bell and Labuza, 1991a,b; Tsoubeli and Labuza, 1991; Skwierczynski and Conners, 1993). The U‐shape pH−rate profile generated from aspartame solution data resembles the profiles of other pharmaceuticals (Conners et al, 1986), including ampicillin (Hou and Poole, 1969).…”