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Unpuckering the Persimmon

based on 4 ratings
Author: Cy Ashley Webb
Type

Biology

Grade

5th – 8th

Difficulty of Project

Easy

Cost

$15.00 for fruit, saran wrap, iron solution, and poster board

Safety Issues

Adult supervision may be needed when the student uses the oven.

Material availability

American and Hachiya persimmons are readily available in most parts of the country in Autumn.

Approximate time to complete the project

Two weeks

Objective

The project is about exploring astringency in persimmons and how that astringency can be removed.   By examining ripe and unripe fruit treated with an iron solution, the student will compare the effect of tannins when they are diffused throughout an unripe fruit and when they are bound up in a ripe fruit.  By forcing the projection of acetaldehyde, students will learn how how tannins can be bound up – and thereby “defanged”.

Project Goal

The goal is to examine astringency in food products and ways of minimizing that astringency.

Materials and Equipment

  • Persimmons (get the American or Hachiya persimmons.  Other types will not work!)   If you live in a place where persimmons grow, you can use the fruit on your trees.)
  • Iron solution
  • Magnifying lens (optional)
  • Baking soda
  • Saran Wrap
  • Oven

*Almost all of these materials can be found at the grocery store.  An iron solution can be found in plant nurseries or aquarium stores.  In a pinch, ground iron filings can be used instead.

Introduction

Background information

American persimmons are commonly found hanging on trees in the autumn months. When unripe, these orange spheres are so astringent that they are inedible.  The ripe fruit is tasty, but has not been used commercially because the fruit becomes increasingly mushy as it ripens.  It is highly desirable to find a way to ripen this fruit while maintaining a nice firm texture so that the fruit can be packed and shipped.

A class of chemicals called tannins is responsible for this astringent taste.  While ripe and unripe fruit both have roughly the same amount of tannins, the tannins in ripe fruit get bound up so they cannot react with the proteins on one’s tongue and saliva.

Research Questions
  • What makes persimmons so astringent?
  • Can the astringency be removed?
  • What effect does oxygen have on the ripening process?
  • What effect does acetaldehyde have on the ripening process?
Terms, Concepts and Questions to Start Background Research

Unripe persimmons are inedible because of the tannins that are diffused throughout the fruit.  This tannins cause proteins in the saliva and tongue to coagulate.  This coagulation of proteins produces the puckery, furry taste in the mouth that we refer to as astringency.  This also happens with unripe bananas, some red wine and tea.

As ripening takes place, the tannins get bound up in storage cells.  This prevents the reaction in the mouth from taking place. When fruit is deprived of oxygen, the fruit uses up the remaining oxygen and produces carbon dioxide.  This carbon dioxide helps the fruit make acetaldehye, which, in turn, causes the tannins to move into storage cells.  This process can be speeded up at warm temperature (but not so warm as to damage the fruit!).

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