Theoretical calculation and experimental validation of ammonium molybdate concentration for fruit ripeness indicator label

Abstract

It is indicated from the previous research that indicator label of fruits ripeness made from ammonium molybdate does not change color according to fruit maturity. The color change in the ripeness indicator label is due to the reaction between ethylene gas (C2H4) emitted from fruits and ammonium molybdate [(NH4)6Mo7O24.4H2O] added into the label. The reaction produces molybdenum blue that turns the color of ammonium molybdate from yellow to blue. This research is approached based on the theoretical calculation of the requirement of ammonium molybdate as a change color in the label and then it is validated in the laboratory. Theoretical calculations of ammonium molybdate reaction with ethylene gas are based on stoichiometry. The result shows that 1 gram of ammonium molybdate reacts with 0.136 gram ethylene gas. The oxidation number of Mo decreased from Mo(VI) in the form of [Mo8O26]4- to Mo(V) in the form of [Mo8O22(H2O)2]4-. The experimental validation in this study is carried out by exposing the label containing ammonium molybdate with ethylene gas into tightly closed jar. At the beginning of the storage, the label was yellow but at the end of the storage, the label color changed to reddish brown either for the sample exposed with ethylene or without ethylene. This research is continued by increasing the RH of the jar to 85% and the result shows that the label turned green at the end of storage. The performance of the label as ripeness indicator is also tested by sticking label in the jar where 1 kg of banana had been previously stored. The label indicates change in color from yellow to dark blue thus it is concluded that the label resulted from this research is potential to be used as ripeness indicator for fruits.