Course:FNH200/Projects/2024/ Avocados

Introduction

Avocados, also known as Alligator Pears, are pear-sized fruits with textured skin and a large pit in the middle. Wild avocados originated from Mexico approximately 10,000 years ago before their domestication by the Mesoamerican tribes. The avocado tree thrives in tropical, humid environments with little wind or frost. As demand grows, concerns for water strains in neighbouring areas grow as well as environmental concerns regarding excessive land usage and deforestation.

Today, avocados have exploded in popularity in the last several decades due to their usage in Mexican cuisine and other international delicacies, as well as widespread knowledge on their health benefits and delicious taste.

Nutritional and Chemical Profile

Nutrition Facts
Serving Size: 1/2 Avocado (101g)
Calories (kcal)	161
Fat (g)	15
Carbohydrates (g)	9
Dietary Fibre (g)	6.7
Sugar (g)	1
Protein (g)	2
Calcium (mg)	12
Iron (mg)	0.6
Sodium (mg)	7
Potassium (mg)	487
Magnesium (mg)	29
Phosphorus (mg)	52
Vitamin A (RAE)	7
Beta-Carotene (mcg)	62
Folate (DFE)	81
Vitamin C (mg)	10

Health Benefits

Avocados are a nutrient-dense food with a unique lipid profile. These lipids are considered 'healthy fats' compared to their saturated and trans fat counterparts. The fats in avocados primarily come from monounsaturated fatty acids (MUFAs) and polyunsaturated fats (PUFAs) with MUFA oleic acid as the predominant lipid in avocados. Unsaturated fats promote cardiovascular health and have been linked to a reduction of cholesterol. Other phytochemicals in avocados alongside MUFAs & PUFAs contain antioxidant properties which can prevent neurodegenerative diseases. Interestingly, research is underway to investigate the phytochemical properties of the avocado peel and ways reuse the waste.

Ripening of Avocados

Avocados are a climacteric fruit which can continue to ripen after harvest, unlike non-climacteric fruits. Fruit ripening is determined by the rate of ethylene production. Their role is to regulate the rate of the fruit ripening process. Ethylene's role in fruit ripening allows the avocado to change its characteristics. The avocado peel darkens while the flesh tenderizes. Aromatic volatiles of the avocado develop contributing to the buttery taste. This allows us to choose between softer ripe avocados versus hard unripe avocados at the grocery store.

Farming and Production

Avocado Farm

Avocados are known for having shallow yet widespread root systems to maximize rainfall collection. Avocado farming thrives when soils are well drained and planted on slopes to avoid water logging. Avocado trees start producing fruit in their third to fifth year and peak in production at around 10 years. Depending on the cultivar, avocados are typically harvested by hand in late winter or early summer and are ready to be picked when they become dark green and yield to light pressure.

Pests and Diseases

Thrip

Over the lifespan of an avocado tree, numerous pests damage the leaves and fruits of the tree. Thrips and mites are common once the avocado tree matures. These pests can cause root rot which leads to wilting and tree decline. Fungal diseases like anthracnose can also cause black spots to develop on the leaves and fruit. Common pesticides used to combat this are insecticides including Spinosad and Abamectin to control thrips, mites, and fungicides.

Post Harvest

After harvesting, avocados are handled gently to avoid bruising, then sorted and graded by size and quality. The avocados should not reach a core temperature above 26° C when transported to the facility where it is precooled and stored. Once it reaches the facility, it should be cooled and stored in temperatures between 4.5°C to 5.5°C. This slows ripening, with controlled atmosphere storage further extending shelf life (see below).

Approaches to Storage

Controlled Atmosphere Storage (CAS)

Avocados in Controlled Storage

Similarly to modified atmosphere packaging (MAP) where levels of oxygen, nitrogen, and carbon dioxide are altered before packaging, controlled atmosphere storage follows a similar process. MAP alters the vacuum-sealed packages' environment but not the external storage environment. CAS alters the external storage environment surrounding the product by adjusting levels of oxygen, nitrogen and carbon dioxide. By reducing the oxygen exposed to the avocados, the spoilage time slows down, and it remains unripe for a longer duration. When avocados oxidize, enzymatic browning occurs in which the phenols in the avocado react with the enzyme polyphenol oxidase that polymerizes phenols into brown pigments.

Food-Grade Coatings

Coated Avocados vs Non-Coated Avocados

Due to the large moisture content in avocados and their penetrable skin, they are easily infected by fungal spores, which make the food unsafe for consumption. Fungicides have been linked to intestinal diseases, kidney failures, and reproductive issues in women. Recently, scientists have developed a new biopolymer coating that is edible, and safe for human consumption comprised of proteins, lipids, and natural polymers such as cellulose. These coatings have been effective at creating a separation between the skin of the avocado and the environment around it. This helps increase the shelf-life of the fruit and slow down overall microbial growth within the avocado.

Different Processing Techniques

Freezing

Frozen Avocados without proper packaging

When avocados are frozen, they retain most of their nutrients including Vitamin A and Vitamin E. Due to its exposure to oxygen, Vitamin C levels decrease slightly, as it is the most sensitive to temperature changes. In general, most of the flavour in avocados is retained during freezing if properly stored. Proper packaging is required to prevent freezer burn which can lead to discolouration and dryness.

Heating

The high volume of water content in avocados allows them to soften when exposed to heat. This may be ideal in cooking scenarios, but unfavourable as a spread on toast or mashed in guacamole. Heating avocados can cause enzyme deactivation leading it to spoil and become unfit for consumption. While certain vitamins are heat sensitive, others, such as Vitamin E and K, along with potassium are generally heat stable.

Innovative Uses of Avocados

Skin Care

Avocados are commonly used daily in spas and clinics around the world. Vitamins E, A, and K help retain moisture and offer exfoliating benefits. Furthermore, avocado oil is often found in multiple face moisturizers due to its hydrating benefits. Used on wrinkles and other aging signs, the antioxidant properties of Vitamin C and E can help limit exposure to oxidative effects. Avocado oil is also used regularly in hair products due to the fatty acids found in avocados. These acids can help promote healthy growth and reduce overall dryness and frizz.

Avocado Supplements by Purare Health

Pharmaceuticals

Recently, avocado oil has been infused into topical ointments due to its benefit moisturizing and reducing inflammation of the skin. As well, certain bioactive compounds such as polyphenols and carotenoids have shown to have anti-cancer benefits and are currently being used in preliminary studies using anti-inflammatory drugs. The physical properties such as the seed, leaves, and the fruit are used in herbal medicine to lower cholesterol levels and increase sexual drive due to its large fiber content.

Potential Exam Questions

Questions

Avocados are a [climacteric / non-climacteric] fruit that relies on the chemical release of [polyphenol oxidase/ ethylene/ ascorbic acid] to ripen.

Answers

Avocados are a climacteric fruit that relies on the chemical release of ethylene to ripen.

Reasoning:

Learning how fruits ripen depending on their climacteric status is a useful skill to have in everyday life (storing climacteric bananas in a paper bag to promote ethylene concentrations) It will act as a tool to guide students on whether fruit can ripen after purchasing from the produce store and a general mechanism of ripening.