A way to measure ripeness of a fruit

A way to measure ripeness of a fruit

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I'm doing an experiment how fast fruits ripen and decay

I'm wondering how to measure the ripeness of a fruit(banana, mango, tomato, kiwi etc.) so that I will get a quantitative results.

I have looked at using penetrometer to see how squishy it is. Is there any other ways to do it?

If not, I'm thinking of getting qualitative results. Is there any tips of making good qualitative results?


Sorry, I am not sure if this falls into Biology category

Asides from just eyeballing the change in color/consistency, Wikipedia suggests using iodine for a qualitative measurement (though without reference):

Iodine (I) can be used to determine whether fruit is ripening or rotting by showing whether the starch in the fruit has turned into sugar. For example, a drop of iodine on a slightly rotten part (not the skin) of an apple will stay yellow or orange, since starch is no longer present. If the iodine is applied and takes 2-3 seconds to turn dark blue or black, then the process of ripening has begun but is not yet complete. If the iodine becomes black immediately, then most of the starch is still present at high concentrations in the sample, and hence the fruit hasn't fully started to ripen.

A quantitative method applicable to many kinds of fruit is going to be tricky. If you have a spectrophotometer you could measure the changes in light absorption as the fruit ages. You will probably want to measure the absorptions of control fruits as they age and then compare them to fruits from whatever experiment you perform.

Another possibility is measuring ethylene and/or carbon dioxide production. As fruits ripen they produce more of both these gasses, but this increase does not follow a neat linear correlation with time to put it lightly. Non-climacteric fruits, if you use them, may also be problematic here as they do not show such increase in gas production.

  1. Merzlyak, M. N., Gitelson, A. A., Chivkunova, O. B., & Rakitin, V. Y. (1999). Non‐destructive optical detection of pigment changes during leaf senescence and fruit ripening. Physiologia plantarum, 106(1), 135-141.
  2. Burg, S. P., & Burg, E. A. (1962). Role of ethylene in fruit ripening. Plant Physiology, 37(2), 179.

Agricultural and Related Biotechnologies

4.29.5 Cell-Wall Metabolism and Fruit Ripening

Fruit ripening is associated with cell-wall metabolism in tomato. Changes in cell walls during ripening include decreases in cell–cell adhesion, changes in turgor pressure, and modification of cell-wall components such as pectins and hemicelluloses. Plant cell walls are made up of cellulose microfibrils that are incorporated into a network of hemicellulose fibrils along with a network of pectins that secure adjacent cell walls. 41 The pectin-rich region of the middle lamella of the cell wall undergoes modification along with partial destabilization which results in a loss of cell cohesion. The loss of cell cohesion also contributes to the liquification of the tomato locules and softening of the pericarp. Originally, it was believed that polygalacturonase (PG) was the major contributor to tissue softening during ripening. PG is involved in numerous processes in plant growth and development including ripening and is encoded by a family of genes in tomato. PG in tomato makes up approximately 1% of the total mRNA in ripening fruit. Antisense lines of PG exhibited an increase in degradation of the pectin compounds but did not result in a change in the softening of the transgenic fruit. In addition, overexpression of PG in the tomato nonripening mutant rin resulted in an increase in PG activity, but significant changes in softening of the fruit. These results indicated that modification of cell walls as related to softening during ripening is more complex than first believed (reviewed in Ref. 22 ).

Upon discovery that PG was not the sole enzyme involved in fruit softening, examination of further cell-wall enzymes was undertaken. In tomato, cloning of these enzymes involved in cell-wall modification point toward an increasingly complex process involving changes in the ultrastructure of the cell wall and not only pectin degradation as originally postulated. 41 The enzyme pectinmethylesterase (PME) has been shown to be involved in removing methylester groups from pectin in fruit cell walls in turn allowing PG to access its substrates and formation of Ca 2+ cross-linked gel structures. 41 Transgenic lines expressing the antisense version of PME yielded lines that exhibited less than 10% of the normal PME activity and resulted in production of cell-wall extracts that contained higher-molecular-weight pectins. However, these same transgenics displayed no discernible changes in softening of ripening fruits indicating that like PG, PME alone does not account for the dramatic textural changes that are characteristic of ripening tomato fruit. 46

The β-galactosidases (β-Gal) and α-arabinosidase (α-Ara) enzymes are believed to be involved in the disassembly of additional cell-wall polymers and are encoded by large gene families. These enzymes may contribute to cell-wall modification and disassembly during ripening by cleavage of side chains to allow for other enzymes such as PG access to their respective substrates. At least seven of these genes have been identified in tomato, six of which have been shown to be expressed during fruit ripening. Despite this fact, the only β-Gal gene found to have upregulation during normal fruit ripening was TBG4. In the rin and nor (non-ripening) mutants, expression of TBG4 was shown to be greatly reduced. Suppression of two other genes (TBG1 and TBG3) did not result in any change in softening during ripening. By contrast, suppression of TBG4 did show a small delay in the softening of ripening tomato fruit (see Ref. 43 , reviewed in Ref. 8 ).

Another group of cell-wall proteins called expansins, which are a group of integral cell-wall proteins originally discovered from their involvement in extension of cell walls in cucumber, have been extensively characterized in tomato. 41 Expansins are capable of causing stretching and loosening of isolated cell walls and are involved in disruption of hydrogen bonds that exist between polymers within the cell-wall matrix. 8 The expansin family is further divided into two groups, the alpha and beta expansins. In tomato, a number of expansin genes have been characterized and found to be expressed in various stages of fruit development and ripening. One alpha expansin, LeEXP1, has been found to be expressed at the onset of ripening and further accumulates to high levels during ripening. In addition, upon treatment of an ethylene inhibitor (2,4-norbornadiene), expression of LeEXP1 decreases and therefore appears to be regulated by ethylene during ripening. 40 Three tomato mutants, rin, nor, and Nr, exhibit decreased softening in the fruit. Expression of LeEXP1 was found to be decreased in each of these mutations again indicating a role for ethylene regulation of LeEXP1 as well as regulatory pathways characterized by the rin and nor mutations. Transgenic plants overexpressing LeEXP1 exhibited an increase in the depolymerization of the matrix of hemicellulosic xyloglucans (see Ref. 11 , reviewed in Ref. 8 ). Suppression of LeEXP1 expression in transgenic tomato plants resulted in fruit with reduced softening by disassembly of the pectin network but had no measurable effect on other cell-wall components.

The endo-1,4-beta-glucanases (EGases) have been implicated in numerous plant processes including organ abscission and ripening of both nonclimacteric and climacteric fruit. Several EGases have been isolated from various plant species including tomato. 29,40 The β-glucan linkages of xyloglucan (XyG), a hemicellulose that is part of the bridge between cellulose microfibrils, are targeted by EGase. 8 In tomato, EGases are encoded by a large family of genes, two of which LeCEL1 and LeCEL2 showed expression in the abscission zones of flowers as well as ripening fruit. 29 These genes exhibited an increase in expression at the start of ripening indicating ripening-related function of modification of fruit cell walls. Antisense transgenic lines of LeCEL1 exhibited a decrease in expression of LeCEL1, but did not show any changes in softening related to ripening. By contrast, these transgenic lines did show a decrease in abscission of flowers due to decreased expression of LeCEL1. 30 These results are similar to what is seen when suppressing expression of LeCEL2. These transgenic lines showed no change in ripening related softening but did show an increase in the strength of the abscission zones of flowers. 12 Whether or not compensation by other family members accounts for the absence of softening phenotypes in these transgenics remains uncertain. Additionally, the exact role the EGase may play during fruit ripening remains to be determined.

The xyloglucan endotransglucosylase (XET or XTH) is another candidate enzyme for involvement in cell-wall disassembly during fruit ripening. Originally purified from Nasturtium seed, this enzyme is involved in cleavage of internal β-1,4 glucan linkages of the xyloglucan backbone. In tomato, several genes responsible for expression of XTHs have been identified. Furthermore, XTHs have also been cloned from species such as grape, pointing to a role in both climacteric and nonclimacteric fruit ripening. A pair of genes encoding XTHs in tomato have been identified in young green fruit tissue during expansion (LeEXGT1) and in ripening fruit tissue (LeEXTB1). 17 LeEXGT1 overexpression resulted in increased levels of mRNA along with an increase in fruit size. This result points to a role for LeEXGT1 in expansion of the whole fruit during development. Driven by the fruit-specific PG promoter, suppression of LeEXTB1 exhibited no significant changes in softening during ripening. The lack of discernible changes in modification of the cell wall in response to suppression and/or overexpression of XTHs could again be due to compensation by other family members or these enzymes may not play a significant role in fruit ripening as first anticipated. 17

Recent advances in cell-wall biology in relation to fruit ripening have pointed out the immense complexity of ripening fruit cell-wall metabolism. Many enzymes are encoded by multigene families which will likely affect the ability to discern which genes are most intricately involved in the ripening process though rapid accumulation of genome sequence and functional genomics tools for tomato should assist in teasing apart this complicated aspect of fruit biology.

Nondestructive methods for determining the firmness of apple fruit flesh

Nowadays, many researches have been accomplished on the attributed quality assessment of agricultural products. Fruits have significantly contributed to these researches because of their high production and consumption, worldwide. In this paper, the nondestructive instrumental researches in the field of firmness assessment for apple fruit discussed. These researches are important for all production and distribution chain activists such as farmers, insurance companies, packaging and transportation companies, wholesalers and retailers. These studies can be used for examining texture quality, predicting the right time to harvest fruits and classifying them according to the level of ripeness and detecting the apparent and internal defects of the fruit. The apple flesh firmness measurement methods consist of acoustic and mechanical vibration methods, optical methods such as hyperspectral scattering imaging, near infrared, ultrasound and other methods. The destructive puncture test method commonly used as a reference method. Nondestructive methods are accurate and quick that is suitable for online applications. Recently, the use of artificial intelligence methods and data fusion techniques to increase the accuracy of quality measuring of the products has been considered that in the future we will see further development of these methods in measuring the firmness of the apples.

Fruit ripening phenomena--an overview

Fruits constitute a commercially important and nutritionally indispensable food commodity. Being a part of a balanced diet, fruits play a vital role in human nutrition by supplying the necessary growth regulating factors essential for maintaining normal health. Fruits are widely distributed in nature. One of the limiting factors that influence their economic value is the relatively short ripening period and reduced post-harvest life. Fruit ripening is a highly coordinated, genetically programmed, and an irreversible phenomenon involving a series of physiological, biochemical, and organoleptic changes, that finally leads to the development of a soft edible ripe fruit with desirable quality attributes. Excessive textural softening during ripening leads to adverse effects/spoilage upon storage. Carbohydrates play a major role in the ripening process, by way of depolymerization leading to decreased molecular size with concomitant increase in the levels of ripening inducing specific enzymes, whose target differ from fruit to fruit. The major classes of cell wall polysaccharides that undergo modifications during ripening are starch, pectins, cellulose, and hemicelluloses. Pectins are the common and major components of primary cell wall and middle lamella, contributing to the texture and quality of fruits. Their degradation during ripening seems to be responsible for tissue softening of a number of fruits. Structurally pectins are a diverse group of heteropolysaccharides containing partially methylated D-galacturonic acid residues with side chain appendages of several neutral polysaccharides. The degree of polymerization/esterification and the proportion of neutral sugar residues/side chains are the principal factors contributing to their (micro-) heterogeneity. Pectin degrading enzymes such as polygalacturonase, pectin methyl esterase, lyase, and rhamnogalacturonase are the most implicated in fruit-tissue softening. Recent advances in molecular biology have provided a better understanding of the biochemistry of fruit ripening as well as providing a hand for genetic manipulation of the entire ripening process. It is desirable that significant breakthroughs in such related areas will come forth in the near future, leading to considerable societal benefits.

Fruit Ripening: Meaning, Factors and Controls | Plant Physiology

There are several developmental phases through which the fruit passes and fruit ripening is one of them. In fact, ripening begins moment the growth of the fruit is completed. Fruit maturity is a stage of fruit harvesting while fruit ripening is a stage of fruit consumption.

The fruit ripening is associated with many visible changes in the colour, the flavour and the aroma. Thus, the fruit is ready for eating purposes. Fruit ripening is a type of ageing and many people prefer to call it “fruit ageing” than fruit ripening. In many fruits the ripening occurs after picking or the process is hastened after picking. Ripening processes are of degradative nature.

Studies in recent years have shown that several biochemical processes must occur sequentially. However, these processes may not be linked with each other.

Factors Affecting Fruit Ripening:

In the following some of the important factors affecting fruit ripening are described:

The visible changes in the fruit leading to ripening are accompanied by a rapid increase in respiration. This process is called climacteric and is distinctly visible in many fleshy fruits like apple, banana, apricots, papaya, tomato etc. However, fruits like figs or cherries do not show climacteric.

This does not mean that the non-climacteric fruits always have low rate of respiration. Some of the compound fruits in fact have high activity of respiration. In general climacteric fruits are rich in carotenoids whereas non-climacteric fruits contain anthocyanins. In apple once the climateric begins the free fructose disappears from the cytoplasm due to phosphorylation.

Simultaneously there is a change in tonoplast permeability which presumably permits movement of fructose from the vacuole to the cytoplasm. Thus, there is an increased respiration. The alternative explanation is that the rate of respiration is regulated by ADP. Thus respiration rate in low if ATP/ADP ratio is high.

The climacteric rise in respiration results from a high energy requirement in the initial stages of fruit ripening. The respiration is enhanced when ATP is split and level of ADP rises. Tomato fruits when sprayed with 2, 4- DNP are prevented from ripening.

One of the factors inducing increased respiration is natural un-couplers of oxidative phosphorylation. Climacteric fruit extracts did act as un-couplers of oxidative phosphorylation. The present thinking is that increased respiration may be attributed to high energy requirements in ripening.

Tracer studies have shown that in several fruits increased RNA synthesis accompanies fruit ripening. Most of the evidence is based on assays of the rate of incorporation of RNA precursors and indicates that RNA synthesis includes mRNA and is enhances during early part of climacteric rise.

In picked up apples about 50% RNA increased at the initiation of the climacteric increase. When the climacteric is high the increase in its synthesis does not occur.

In general, new synthesis of RNA seems to be essential for the ripening process. Pears sprayed with Act.D did not ripe. The rise in the RNA concentration is followed by an increase in the protein content because of new synthesis. Indeed the synthesis of new proteins is essential for the ripening of many fruits.

When the mature, unripe banana and pears were sprayed with cycloheximide, ripening was inhibited. This was especially so when it was administered during early stages. It is assumed that enzymes involved in ripening were synthesized during the early stages.

Changes in the pattern and activities of several enzymes are reported during fruit ripening. In general, several hydrolytic enzymes increase. These include polygalacturonase, cellulase, pectin methyl esterase, etc. Some of the enzymes soften the fruits and bring about changes in taste as well. The sweetness in several fruits is caused by breakdown of starch into sugar. Sometimes fruits abound in free fatty acids.

However, the importance of several enzymes in ripening of fruit is not clear. This category includes lipidase and peroxidase. It is believed that these enzymes may be involved in the biosynthesis of ethylene. Sometimes different isozymes are associated with fruit ripening.

Increase in chlorophyllase, lipase causes breakdown of chlorophyll and free fatty acids, respectively. Similarly increased lipoxidase is also reported. Large increase in acid phosphatase activity parallels the climacteric in mangoes. In several fruits enzymes of glycolysis, oxidative processes—HMP shunt and citric acid cycle also increase.

Fruit ripening is also accompanied by dramatic changes in its colour e.g., in tomato following sequence of colour changes are observed:

The red colour is due to lycopene. Carotenoid formation occurs when chloroplast is converted into chromoplast. However, not in all the cases the change in fruit colour is associated with the formation of carotenoids.

On the contrary in many fruits anthocyanin is synthesized during ripening as in apple. The present thinking is that synthesis of carotenoids and anthocyanin in ripening fruits is regulated by phytochrome system.

v. Effect of Potassium Nutrition on Fruit Ripening:

In tomato fruit increased potassium (K + ) nutrition causes an increase in the concentration of organic acids, in particular citric and malic acids. It may be recalled that tomato is a climacteric fruit so that the pre-climacteric respiration minimum is followed by a peak during which the rate rises by 110—250%.

When the plants are supplied with high concentrations of K they have reduced rate of respiration especially during the climacteric phase. There is great accumulation of oxaloacetic acid (OAA) which is also increased by K application.

This increase is due to the oxidation of malate by malate dehydrogenase and can be inhibited by malate and succinate oxidation by tomato fruit mitochondria. The rate of endogenous concentration of OAA could be controlled by the rate of transamination with L-glutamate through the action of GOT.

Fruit ripening is also retarded by osmotic water intake and by washing out of some unidentified substances. Besides the climacteric respiration, other characteristic metabolic pathways can be seen. For instance, in ripening mango fruits aspartate and glutamate decrease, while α-aminobutyrate increases.

Together with changes in enzyme activities, the following metabolism of aspartate and glutamate must occur:

This metabolism indicates that the most significant amino acids are decomposed. This may partly explain why protein synthesis ceases during ripening.

Hormonal Regulation of Fruit Ripening:

As many as five types of plant hormones are known to regulate fruit ripening. In recent years occurrence of IAA in fruits has been demonstrated beyond doubt. While young seeds are the main site of IAA synthesis, in the mature fruit it is synthesised in the fruit flesh. In fact auxins slow down fruit ripening except in some cases where they may quicken.

Perhaps auxins prevent ethylene formation in fruits. Obviously auxins must be degraded endogenously through series of enzymes like IAA—oxidase, etc. to control fruit ripening. Moment the auxins are degraded the fruit tissue becomes sensitive to ethylene.

Very little is known about the endogenous cytokinin content and its metabolism in fruits. On the basis of their function in the leaves, they possibly contribute in keeping the protein and chlorophyll content constant.

The effect of gibberellins in a way is comparable to auxins and cytokinins. Most studies have been done on oranges where GA inhibits degradation of chlorophyll/and delay carotenoids accumulation. Thus pigment formation is delayed. Similarly banana fruits sprayed with GA do not undergo yellowing even though other processes occur normally.

In large number of fruits, before the ripening is ultimately achieved there is accumulation of ABA (Fig. 25-2). Perhaps this phytohormone regulates fruit ripening. In apples after a week of harvesting ABA content increases many times. ABA concentration is very high in the inner part of the green fruit flesh of tomatoes.

It may be mentioned that tomatoes ripen in a centrifugal direction and as the process progresses the relationship is reversed. Thus in ripened part ABA level falls down. In the following diagram (Fig. 25-3) a relationship between phytochrome, ABA and lycopene content of ripening tomatoes is given.

It will be observed that with the red light illumination of tomatoes, ABA content rises several-fold in first few days and then declines. The present thinking is that ABA triggers lycopene synthesis.

Ethylene is an important hormone concerned with ripening. Fruits fail to ripen in the absence of ethylene. It is shown that ethylene probably brings about the climacteric. Similarly, non-climacteric fruits once treated with ethylene also show increased respiration. Perhaps difference between climacteric and non-climacteric fruits may be due to ethylene production. Ripening can be induced only when auxin is degraded by IAA oxidase, etc.

In view of the reported effect of ethylene in altering the proportion of individual tRNA species, ethylene may be regulating translation of mRNA and thus initiate ripening. In tomatoes, exogenous application by ABA enhances ethylene production.

Whether ABA induces ethylene synthesis in vivo is not clear. Light is also shown to induce ethylene formation. For instance, red light induces ethylene formation while FR slows it. Obviously the phenomena of fruit ripening appear to by a set of highly complex physiological events.

It may be stated that ethylene formation in plants is not exclusively induced by light. It is also produced when a tissue is injured, or diseased or due to physical and chemical stresses. Even action of some metal ions e.g. Cu ++ and Ca ++ causes ethylene formation. Most studies are available in tomato.

In the following scheme a possible relationship between phytochrome and some hormones in fruit ripening has been elucidated:

The above scheme provides tentative relationships between various components though precise relationships between various components though precise relationship of ABA and ethylene is not well understood. There are reports that ethylene causes increase in ABA level and the latter hormone might initiate fruit ripening by stimulating ethylene production.

Flesh Softening:

During ripening there is breakdown of insoluble protopectin into soluble pectic compounds. The process is enzymes mediated. No detailed mechanism of softening is known. During ripening there is shortening of the polymer chain length, demethylation of carboxyl groups and deacetylation of hydroxyl groups.

All these affect cell wall consistency through change in the bonding with associated cell wall constituents e.g., cellulose, hemicellulose.


Most climacteric fruits possess starch as a storage reserve. This is broken down into soluble sugars due to enzymes. Thus fruit attains sweetness.

Loss of Astringency:

In some fruits which are unripe, there is abundance of tannins of low molecular weight (polyphenols) which react with proteins e.g. banana or sapota. When eaten they give astringent taste. With ripening, tannins polymerise into large molecules and lose their capacity to react with protein. Instead they get trapped in the cell.

Sourness of fruits is due to organic acids. The taste is determined by the ratio of sugars and acids. With increased ripening, the total activity decreases. However, in banana, the acids increase on ripening.

Aroma and Flavour:

Ripe fruits have intense aroma and flavour. Aroma is due to the volatile chemical compounds which are enzymatically synthesised and emitted. These volatile compounds are esters and lactones, alcohols, acids, aldehydes, ketones, acetals, phenols, ethers, etc.

Controlled Ripening:

Harvesting does not indicate the end of a fruit life. Several of the fruits can be successfully stored up to several weeks by controlling mechanical injury, transpiration, respiration, decay and physiological breakdown. Several physiological and chemical agents are employed to slow down metabolic rates in fruits.

By refrigeration of fruits, storage period is enhanced. It helps in two ways: slowing down respiration due to low temperature and checking microorganisms development. Temperature also influences endogenous ethylene production.

Recently controlled atmosphere (CA) storage is used in collaboration with refrigeration. These processes maintain high quality of fruits. The technique is affectively used in storing apples, citrus, etc. The CA is affected by increasing CO2 in the atmosphere or reducing O2 levels.

Similarly, some fruits are stored under low pressure. It is a new approach in the long-term storage of fruits. In this method, ethylene evolved is removed, and the partial presence of oxygen is lowered. This slows down the ripening.

Studies at the Bhabha Atomic Research Centre, Mumbai have demonstrated the potential of low- dose gamma irradiation for retarding ripening in mango, papaya and banana. Irradiation also increases pigmentation.

Sometimes fruits are dipped in wax emulsions or plastic films. Even treatment with GA retards ripening.

Artificial Fruit Ripening:

Ethylene is currently used commercially to induce ripening in mangoes, tomatoes, banana, and even degreasing citrus fruits. Temperature affects the process of artificial ripening with ethylene. This gas merely removes chlorophyll and unmasks yellow and orange pigments.

In some fruits, there is synthesis of these pigments also. In fruits with pronounced climacteric, 0.1-100 ppm ethylene is effective when applied in the pre-climacteric stage. There are several sources of ethylene (ethrel, CPTA). Sometimes acetylene and carbon monoxide are also used for artificial ripening of bananas and mangoes.

Hot water dip treatment of mangoes enhances ripening and colour development. This also lessens microbial growth. The ripening is independent of maturity of fruit. In order to have characteristic taste, only optimal mature fruits should be artificially ripened.

A4. Threat Reduction to Internal Validity

Threats to the inner validity of the analysis have been reduced by the simple testable question, the properly recognized variables, the control for outdoor influences, and the sound experimental treatment.

MATURATION The test will be started and completed in one day, and can have a maximum of two time. That will allow sufficient time for every single trial to be conducted carefully as well as for the utensils to be cleansed - while ensuring that you will see virtually no time for the subjects to improve before measurements.

REPEATED MEASUREMENTS The experiment will be repeated 3 x for each kind of strawberry, with a fresh set of materials each and every time, equating in exactly nine trial runs. Each sample will be removed after email address details are recorded, before the next trial was done - nothing of the samples will be reused, nor will they touch each other.

INCONSISTENCE IN INSTRUMENTATION In every trial run, the measurements will be studied using the same graduated test tube, goblet, jar, and calculating spoons. Every measurement made will be studied in ways identical to the one before it, so that the end result of the experiment is not compromised.

EXPERIMENTAL MORTALITY The test is designed such that it can't be completed without all of the subjects, meaning nothing of the subject matter can drop out or be taken away without completely derailing the analysis. This way, the trials will remain the same, and the results will not be compromised.

EXPERIMENTER BIAS The test did not entail and may not come to any result that the experimenter would gain straight from. The experimenter remained objective throughout the analysis.

CONTROLLED VARIABLES There are several controlled factors that limit the factors that could skew the results. The various tools for measurement continue to be the same throughout the studies so that there is no potential for new tools not providing the same results. The quantity of strawberries remains the same - three per trial - so the amount of extractable DNA is not distorted by one trial having more strawberries than others. The quantity of blue dye remains the same throughout the tests so a much larger amount of dye won't make the results seem to be bigger than they are really.

Terms and Concepts

  • Visible light
  • Electromagnetic spectrum
  • Wavelength
  • Reflect
  • Absorb
  • Transmit
  • Light emitting diode (LED)
  • Photoresistor
  • Resistor
  • Resistance
  • Ohms (&Omega)
  • Potentiometer
  • Transistor


  • What are some different ways you can tell when fruits or vegetables are ripe?
  • What are some scenarios where it would be useful to have a machine tell if fruits or vegetables are ripe?
  • Does the resistance of a photoresistor go up or down when more light is shined on it?
  • If you shine a red light at a blue surface (similar to Figure 3), would the photoresistor's resistance be high or low?

Cooperative Extension: Tree Fruits

Most fruits produce a gaseous compound called ethylene that starts the ripening process. Its level in under-ripe fruit is very low, but as fruit develop, they produce larger amounts that speed up the ripening process or the stage of ripening known as the &ldquoclimacteric.&rdquo The level of ethylene and rate of ripening is a variety-dependent process. Some apple varieties such as McIntosh, produce prodigious amounts of ethylene and are difficult to store once this occurs. When harvested after the rapid rise in ethylene, they quickly soften and senesce in storage. Other varieties have a slower rise in ethylene and slower ripening rate. For apples that will be stored longer than two months, it is imperative to harvest them before the level of ethylene begins its rapid increase.

Plums and peaches are also sensitive to ethylene and will continue to ripen after harvest in response to this hormone. Some varieties of plums, such as Shiro, ripen very slowly since ethylene production is suppressed. With these suppressed-climacteric types, fruit may remain under-ripe if harvested too early. Other plum varieties such as Early Golden ripen very rapidly. In this case, harvest should be timed more precisely so that fruit are not over-ripe when they reach the consumer.

To measure ethylene, expensive instruments are needed. This is often done by specialized labs and sometimes by Cooperative Extension to determine if fruit in a general region are still at a stage where they can be stored long-term. Cheaper methods can be used to measure stage of ripeness, but are not as precise as measuring the level of ethylene in fruit.

Methods of controlling ethylene in fruit include preharvest application of aminovinylglycine (ReTain), postharvest application of 1-methylcyclopropene (SmartFresh), cold storage, controlled atmosphere storage, and ethylene scubbing or removal.

Why are fruits so alluring?

Fruits are colourful and flavorful because they want to get eaten! That&rsquos the entire reason for their existence!

Sounds a bit harsh, right? As a matter of fact, for humans and other animals, fruit is something delicious to eat, but for a plant, it&rsquos a means of survival.

The fruit protects the seeds from environmental conditions.

Fruit protect and nourish a plant&rsquos seeds as the seeds mature, the fruit surrounding them ripens, getting bigger, juicier, sweeter, and more colourful. These changes entice the consumers (humans and other animals) to eat the fruit and, with any luck, drop the seed elsewhere, where it can grow into a new plant. Ripening their fruit is a survival tactic used by plants to help them reproduce and multiply.

How to Measure a Banana's Ripeness

Banana plants lend a tropical feel to the garden, but some species, such as Musa basjoo and Musella lasiocarpa are hardy to Zone 6 with winter protection such as pruning and mulch. Bananas are harvested in an unripe state, with the ripening process not fully beginning until they are separated from the banana plant. The flavor and texture of a banana changes as it ripens.

Check the color of the banana. Unripe bananas are typically solid green when harvested, gradually turning yellow as they ripen. Brown spots begin to appear when the banana is ripe, with more of the peel turning brown as it becomes overripe.

Feel the banana to gauge how firm it is under gentle pressure. As starches within the banana convert to sugar during the ripening process, both the banana and its peel become softer. A very firm banana is not quite ripe, while a very soft banana is overripe.

Examine the shape of the banana, paying particular attention to the ridges where the peel sections join together. Unripe bananas have very angular ridges, but these ridges soften and become rounder as the banana ripens.

Smell the banana. Unripe bananas have a slight pleasant odor to them which increases as the bananas ripen and begin giving off ethylene gas. Once fully ripe this odor may start to fade due to reduced ethylene production.


  1. Jadan

    Unmatched message, I really like :)

  2. Fenrikazahn

    Interesting and informative, but will there be something else on this topic?

  3. Voodoogul

    What phrase... super, magnificent idea

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