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STUDIES ON THE INHIBITORY EFFECT ON TYROSINE ON POLYPHENOL OXIDASE IN WATER YAM

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

Polyphenol oxidase (PPO) is an enzyme widely present in plants, animals, and fungi. It plays a crucial role in the browning reaction in fruits and vegetables, which impacts their visual appeal and nutritional quality. Water yam (Dioscorea alata), a staple food in many tropical regions, is particularly prone to enzymatic browning due to the activity of PPO. This browning not only affects the market value and consumer acceptance of water yam but also reduces its shelf life. Tyrosine, an amino acid, has been identified as a potential inhibitor of PPO. Understanding the inhibitory effects of tyrosine on PPO activity in water yam can lead to better post-harvest handling and processing methods, thereby enhancing the quality and marketability of this important crop.

1.2 Statement of the Problem

The enzymatic browning of water yam caused by polyphenol oxidase activity is a significant problem affecting its marketability and consumer preference. Despite the potential of tyrosine as an inhibitor of PPO, there is limited research on its effectiveness specifically in water yam. Addressing this gap is essential to develop strategies for improving the storage and processing quality of water yam.

1.3 Objectives of the Study

The main objective of this study is to determine the inhibitory effect of tyrosine on polyphenol oxidase activity in water yam. Specific objectives include:

i. To evaluate the impact of different concentrations of tyrosine on PPO activity in water yam.

ii. To determine the optimum concentration of tyrosine required to inhibit PPO activity effectively.

iii. To find out the effect of tyrosine treatment on the browning rate of water yam during storage.

1.4 Research Questions

Based on the specific objectives, the research questions are:

i. What is the impact of different concentrations of tyrosine on PPO activity in water yam?

ii. What is the optimum concentration of tyrosine required to inhibit PPO activity effectively?

iii. How does tyrosine treatment affect the browning rate of water yam during storage?

1.5 Research Hypotheses

Hypothesis I:

H0: There is no significant impact of different concentrations of tyrosine on PPO activity in water yam.

H1: There is a significant impact of different concentrations of tyrosine on PPO activity in water yam.

Hypothesis II:

H0: There is no significant optimum concentration of tyrosine required to inhibit PPO activity effectively.

H2: There is a significant optimum concentration of tyrosine required to inhibit PPO activity effectively.

Hypothesis III:

H0: There is no significant effect of tyrosine treatment on the browning rate of water yam during storage.

H3: There is a significant effect of tyrosine treatment on the browning rate of water yam during storage.

1.6 Significance of the Study

This study is significant as it addresses the issue of enzymatic browning in water yam, which has implications for food quality and shelf life. By identifying effective concentrations of tyrosine to inhibit PPO activity, this research can contribute to improved post-harvest handling and storage techniques. This, in turn, can enhance the economic value of water yam for farmers and traders, as well as provide higher quality produce for consumers. Additionally, the findings could be applied to other crops with similar browning issues, broadening the impact of this study.

1.7 Scope of the Study

The study focuses on evaluating the inhibitory effect of tyrosine on polyphenol oxidase activity in water yam. It includes laboratory experiments to test different concentrations of tyrosine and their impact on PPO activity and browning rates. The scope is limited to the post-harvest treatment of water yam and does not extend to field production or other post-harvest treatments.

1.8 Limitations of the Study

The study may be limited by the variability in water yam samples, which could affect the consistency of the results. Additionally, the laboratory conditions may not perfectly replicate real-world storage environments. Access to advanced laboratory equipment and reagents might also pose a limitation, potentially affecting the precision of measurements and outcomes.

1.9 Definition of Terms

Polyphenol Oxidase (PPO): An enzyme that catalyzes the oxidation of polyphenols, leading to browning in fruits and vegetables.

Tyrosine: An amino acid that has potential inhibitory effects on PPO activity.

Enzymatic Browning: A chemical process involving PPO that results in the brown coloration of cut or damaged fruits and vegetables.

Water Yam (Dioscorea alata): A species of yam commonly grown in tropical regions, known for its high nutritional value and susceptibility to enzymatic browning.

Inhibitor: A substance that slows down or prevents a particular chemical reaction or other processes.